Briefly had this problem with my then 5 year old OTTB. Once we started cantering in open fields, he thought "game on". Stopped cantering and worked on nothing but relaxation. Rode him everywhere at the walk. Once he was relaxed at walk, we moved onto trotting which was not an issue. We added cantering with the aid of another horse. My horse will do whatever a mare tells him to do, so we put a mare in front. We would start cantering. When he started to get strong, I would ask for him to soften. If he blew me off and got stronger, the mare in front would throw a block and we would stop, regroup, and start again. Luckily I have a very quick learner. This only went on for a few rides before he started to soften when I asked and no longer need the mare's help. Once I knew he was listening to me, I worked a lot on transitioning within the canter gait. I would go out into the fields, ask for canter, then high canter, then hand gallop, and then work my way back down to normal canter. Worked very well, and I ended up with a very adjustable horse on cross country as a result. He feels me sit taller and comes back to me without question.
You just have to see your distance...you don't have to like it.