Your horses won't canter help

I know three ways:

1.Sometimes using poles will help.

2.you could also try to get your horse into a working trot and make him work hard. trot small circles, figure eights, anything to get him working, and then do whatever you have to to get him to canter, whether its a whip, spurs, ect.(im not saying be violent, but sometimes you just gotta get your point across) and let him rest at the canter. just drop the reins an let him canter where ever he wants. once he drops into a trot, work him again for a while and get the canter again.

3. get into an open place, out of the arena or in a bigger pen and see if the open space frees up his feet a little.

you also might want to look and see if the saddle hurts him. if a saddle is pinching a horse, the canter is where it becomes the most obvious, so if cantering is hurting your horse, then no wonder he doesnt want to.