It sounds like your horse is a bit too balled up. He's got lots of energy and he's used to exerting that energy on the track. My advice? Harness the energy.
Sit deep in the saddle with your knees open and your hands firm on the reins. Try bringing him into frame at the trot, then ask as subtly as possible for the canter. As soon as he transitions, start working to keep him in frame.
Do lots of different exercises at the canter, particularly circles. In other words, give him a direction. Work on extending and shortening the canter stride on the long sides of the arena and through circles to show him that he can lengthen out without speeding up.
I would also work him lots in the round pen. Ask for tons of trot-to-canter and canter-to-trot transitions. He probably has adequate impulsion and plenty of forward momentum; the trick is getting him to even out.
Hope that helps,
ETA: I see that Andi offered a lot of the same advice. Circles are definitely a good thing. Try serpentines, as well, coming down to a halt at every change of direction.