Pursuing the Canter

Syd is a great horse. I'm learning so much about the training scale. But, and there's always a but, isn't there? He won't canter for me. It's a problem I've created and I knew I was creating it while it happened. I just never dreamed it would be so hard to fix. Sometimes he'll pick it up behind and then just crash back into the trot. Sometimes he picks it up easily and it's lovely. Sometimes he just speed trots. And the real frustration comes in because I can't tell the difference between what's going to be a successful transition and what's not. I've tried him on the bit, off the bit, really collected, strung out, from a walk, from a trot, from a halt, from various collections or extensions within those gaits. I've tried a following hand, a supportive hand, a rather restrictive hand (hey, nothing else was working), etc. You name it and I've tried it with this horse. I've given the classical aid for canter, a more western aid of just one leg; heck, I've even tried kicking with a smack of the whip. And you know what, I've been successful at least once with all of those things. But it's not consistent. He knows he doesn't have to canter for me so he does it only if he feels like it. The only way I really to know to fix this is to get quite forceful and given that his reaction to force is to buck and he's 17.2 hh (which makes for a BIG buck), I'm hesitant to start a fight that I may not be able to finish. More frustrating is that other people can canter the darn horse. I'm the only one with this problem. I've created it and I'm going to have to fix it but in the meantime I'm struggling to stay calm and philosophic. So I'm pursuing the canter for as long as the footing holds.