One of the most common questions I hear from gaited horse owners is whether it is all right to canter, or to trot, their gaited horse. Or, can gaited horses canter? In regard to both questions, the answer is, "that depends."
Someone who rides a laterally oriented horse may do well to encourage the horse to canter, as it will teach it how to break up that addictive, lazy habit of pacing or step pacing, and teach it the basics of working off the haunches and rounding up through the back. The stronger and better conditioned the horse, the less likely it is to pace. It's unlikely that an animal with a very strong tendency toward pace would learn to trot before establishing a more square gait, and this would not be as productive as cantering, in any case.
On the other hand, a horse with a strong natural tendency to trot will have difficulty learning to gait if allowed to do so, while encouraging the diagonally oriented animal to canter often leads to a specific gait problem that is difficult to fix, once the habit has been started.
A primary challenge when trying to teach laterally oriented horses to canter is their tendency to cross canter; that is, take up opposite leads in the front and back legs. There is a very strong possibility that a horse doing this will trip itself up, which may result in a very nasty somersault-type tumble for both horse and rider. Therefore, if you canter your horse, but feel as though you're being violently pushed out of the seat of the saddle with each stride, immediately bring the horse to a halt or walk, and start over again. If cross firing persists, then give up teaching the canter until the basics of collection are more well established.
One of the easiest methods for teaching a pacey horse to canter is to ask for the gait on a hill or incline. This gets the horse's weight over its haunches and lightens up the front end, making the strike off for a canter lead much easier. If you have a riding friend with a horse that canters, so much the better - often if a lead horse starts to canter, the horse following behind will come up into that gait as well.
If you have no hills where you ride, then you'll want to begin teaching your horse how to balance its weight more rearward, and round up through the back. This means you're virtually 'collecting energy' through the horse's body. . .which energy can then be utilized for a correct canter take-off. The way to do this is to practice correct half halts. Half halts not only enable the horse to correctly distribute its weight, but over time greatly enhance the animal's overall balance and condition. I recommend that all riders learn this very simple technique, and utilize it regularly.
A half halt is (in brief), when you use your seat, legs and hands to begin to ask for an even halt, but then push the horse on the instant you feel any hesitation. You'll want to be sure to maintain rein contact when you do this, as the idea is to get the horse to balance a greater proportion of weight over his hind legs, while rounding up through the back (this rounding up is called 'vertical flexion,' and is at the heart of correct collection, or engagement.) When you push your horse forward while taking evenly on the reins, the horse - if it is not being ridden in a very stiff frame, and/or uncomfortable tack - will use the increased forward momentum to 'back off' the bit. Then when you push him on while maintaining rein contact, the forward energy will have the effect of rounding up his back (tack permitting). If you release too much rein, the horse and rider's weight will merely fall back onto the forehand. It's as though you brought a burst of energy in through the back door. . .and immediately threw it out the front.
Releasing too much rein - or holding the reins in a death grip - are the most common problems I encounter when teaching riders how to do an effective half halt. Both result in heavy, stiff moving horses. The good news is that, with a little practice you can learn exactly how much rein is needed to initiate, and maintain, an effective half halt. Once you've achieved this, you'll be amazed at how much lighter and more responsive your horse will become to your riding cues - and how well under-saddle training of all kinds is facilitated.
It's important to note here that half halts and vertical flexion should not be expected of horses less than four years of age. The job of learning to balance itself under a rider's weight over various terrain, and respond to basic riding cues, is quite enough for the young green-broke horse. This is why I do not permit horses younger than four years to participate in gait clinics or private instruction. I believe it is imperative that the animal be allowed enough time and experience to master the basics of safely carrying a rider and getting in strong condition before demanding higher level responses. I once had a clinic participant who was having a terrible time getting her (reportedly) 5 y.o. gelding to respond correctly to half halt cues. My clinic assistant was suspicious about the horse's true age. . .checking his teeth confirmed her doubts, as he was barely three years of age. I dismissed the pair from the clinic. If you're in a hurry to ride a gaited horse, then please buy one of an appropriate age - far too many gaited horses are pushed for too much, too soon, and the long-term results are far-reaching, and often devastating.
Now, back to discussing canter! A canter is correctly performed as follows (description on a right lead): The horse sets down the left hind leg, followed by the right hind leg and left foreleg, and then the right foreleg. The true 'leading' leg is always the hind leg and the 'leading' foreleg is on the same side. The leading hind leg sets deeper under the horse than the non-leading leg, and the leading foreleg strides out farther than its counterpart.
After you've perfected and practiced the half halt, you'll discover your horse is more able to learn a correct canter, even on level ground. You initiate a canter by asking for a strong half halt, but with a bit more take on the outside rein (the side of the non-leading canter leg), to slightly tilt the horse's head to the ouside. This simple action helps to lighten up the weight over the front leading shoulder, making a cross canter less likely. Hold your outside leg behind the girth, and hold your inside leg straight and steady. Once the horse has shifted its weight rearward, use your outside leg to vigorously push the horse forward. When the horse starts to spring forward as a result of these cues, lean forward and release some - not all - tension on the reins. With a little practice, this method should encourage a correct canter from even a very laterally oriented horse.
Perhaps you can see how the canter, which requires using diagonal sets of legs - one pair together, one pair in opposition - will help condition and train a pacey horse to break up lateral action.
Now it's another story altogether if your horse is more on the trotty end of the gait spectrum. Such horses find cantering all-too-easy, especially when compared with the hard work of performing a four-beat gait, in good form. Such a gait requires a lot of motion, front to back, through the horse's back - while trotting generally only requires that the horse jump from one set of diagonal legs to the other, requiring much less coordination and effort.
What frequently happens when a trotty horse is permitted to canter is that whenever the rider cues for gait, the horse will attempt to jump into a canter, instead. The rider then checks the horse back, and again asks for gait. . .so the horse 'jumps' into the opposite canter lead. The result of this is that the horse soon learns it can just shuffle on its forelegs while jumping from side to side on its hind legs, and there's very little the hapless rider can do to correct the situation. I call this mish-mash gait the 'cant-a-lope,' and once a horse has developed this habit, it can be very difficult to correct. For that reason it is my recommendation that a diagonally oriented horse never be allowed to canter until the gait has been very well established - if then. If you do decide you'd like to canter your trottier horse, always cue for the canter from the halt or walk, and never from gait (this is true for any gaited horse). Establish very clear, and differing, cues for canter and for gait. I recommend verbal cues such as 'Walk on!" and "Lope!" Be very consistent with your cues, and be sure not to neglect the practice of gait work in favor of cantering, or you may have to go back to square one to redevelop the intermediate saddle gaits.
I also recommend that trotty horses not be permitted to trot until their saddle gait has been well confirmed. Again, this is because we're in the process of building muscle condition and neurological memory for the intermediate gait - allowing the trot during this process may be confusing and counter-productive.
All of this may sound rather complicated when seen in black and white. But when you're on your gaited horse, and have gained a 'feel' for its movements, you'll find this work to be fun and highly rewarding. It will pay off not only in smooth saddle gaits and long term soundness. . .but in the inevitable bond that forms between a horse and an active, conscientious rider.
I wish you many happy and smooth trails!