equestriangirl97 said:

Hey, I would work on trotting him to jumps instead of cantering them. When you do start cantering the jumps, if he gets strong you should make a circle, and if you feel him rushing, make a circle. He will soon learn that he has to calm down to jump. Work on half halts, and on the flat and while just hacking, practice shortening and lengthening his strides in all of the different gaits (walk, trot, canter). Also, working on strengthening your abdominal or core muscles will help. I hope this helps!

While this is a good answer, you have to make sure you don't do it too much or your horse will get into the habit or refusing.

if i were you i would try placing trotting poles on the straight before the jump, this will encourage your horse to keep a balanced pace before the jump and also act as a distraction and make him think about picking his feet up correctly and he will have less of a run up to the fence, hope it helps!

My horse Eric got into this habit when I first began schooling him over jumps and I found that doing circles in front of the jumps and weaving in and out of them. Give it a try and see if it works. Hope this helps xx