One caveat on the “as many canter strides as he can do right” theory. I implemented that years ago. I ended up training my horse that cantering involved 5 or 6 strides. Only. Which was hard to overcome. We still struggle with it a bit. My solution has been the pole work. I set them at 5 stride intervals. We canter over a poll, he takes his required 5 canter strides, then “Oh look another pole” which he will hop and then we canter on.
Solution 2 is to anticipate him breaking, and legging him on for a couple of energetic gallop strides just to take away the idea that when we get too tired to canter right doesn’t necessarily mean we’re taking a break.
Don’t forget you’re always training them to do something. Be careful what you ask for…