How do you stop a pony from bucking when you go into canter?
First if he/she try's to buck while asking for a canter u need to sit back but squeeze at the same time. If you use a different cue do not kick always sit deep in the saddle relax it just might need to let out a couple of bucks. I suggest not using spurs but a mild English riding crop may do the trick to drive the horse forward. Try doing some ground work if he/she bucks while being lunged seek professional help. Also ask your self these questions, Am I warming him up correctly? Am I checking his legs and tack regularly. Is the horse up to date on its shots? If you answer no to any seek help immediately!!!
Make sure you are giving your horse the correct signals. It just may be confused on what signals you are giving them. If you are an inexperienced rider ask one of the bigger, more experienced rider to get on them and see if it isn't (or is) you fault.
Do you carry a stick? If so he might be scared of that, try without it.
Remember, Sit deep in the saddle, lean back slightly and pull his head up if its not the stick and you still carry one, give him a' little tap to tell him off. Also, check his teeth, if they are uneven,it might be that and/or The saddle could be piching/hurting him