Join Date: Sep 2007
Location: Washington State
Make it clear that the trot is not what you asked for and it is not what you want from him. As soon as you cue for canter from walk and he takes off in the jarring trot, bring him up and make him walk politely before asking again rather than to be jounced into canter. If he gets away with taking you into a fast trot before having to canter all of the time, that is what he'll continue to do. He's essentially giving the "wrong answer" to your request and unless you stop him immediately and make it clear that it isn't what you wanted, he'll just assume that it's a "good enough" answer.
Good luck, I hope that makes sense!