Erik, my 17.2hh warmblood, has always struggled with his canter. He's so long and 'lollops' around that it can be quite difficult to get him to engage and create that 'jump' in his stride. So here's my top tips to help improve your horses canter so you'll feel like you're riding your very own Valegro:
Tip no. 1: Transitions both within and out of the pace. These can be really beneficial especially when ridden on a 20 metre circle as it's easier for him to stay balanced. Canter-Trot-Canter transitions encourage him to push with his hind legs, creating more jump. It's important to remember to encourage him to keep pushing forward when doing the transitions but check you don't push him out of balance or you'll find it gets messy and he starts running through your hand!
Tip no.2: Spiralling down from a large circle to a smaller circle. By using this exercise (effectively a leg yield on a circle) it encourages him to 'sit' more on his hind quarters and use his hind legs more effectively. Start off on a 20 metre circle and gradually spiral down to a smaller circle. Never go below 10 meters, then spiral back to 20 meters.
Tip no. 3: Use your 3/4 line! It's important horse's remain straight when in canter as quite often we see horses that canter 'quarters-in'. Test this on your 3/4 line in the school. Coming away from the track, without the support of a wall/fence really tests your horse and your aids. Often many top level riders will rarely ride on the track so to consistently check their horses are straight.
Tip no. 4: Polework. This can be really useful at condensing the canter down and helping him 'sit' more. Take one pole and place it on the ground, take a second pole and place it further down the arena directly in front of the first. Don't be fussy about the length. Pick up a good working canter and ride the line of the two poles, cantering over them. Count the number of strides in-between the two poles (so let's say its 15). Once you've done this a couple of times, canter it again and this time add in an extra stride so try to do it in 16 strides. This shortens the canter and encourages him to 'sit' and use himself more. Be aware this can be quite challenging for your horse, so don't overdo it and take regular breaks. Alternatively, if you don't have access to any poles, pick two points in your arena and do the same. There is a great article on this from Horse & Hound (READ IT >HERE<).
Tip no. 5: Canter leg yield. This is really good at helping to supple your horse and help lift his forehand. Starting on the 3/4 line, keeping your horse straight but flexed to the inside, apply some pressure with your inside leg to encourage him to move sideways back to the track. You can also ride this from the track to the 3/4 line which is slightly more difficult. Make sure your horse knows what you're asking of him, it might be best to start this in walk and trot, so he has a better idea of your aids.