Circles! My guy has a very chargey canter too, I like spiraling in and out on a 20m circle. It helps him balance better and improves bend which in turn controls the speed and the canter is less flat.
Do a bit of extended trot work before asking to canter. Get him using his back muscles and have a nice foreword overreaching trot when you ask. It will halo to have a nice clean smooth transition. ;)
I had a very similar problem with my horse a while ago, there was no impulsion in the canter. By riding "into the bit" with your hands and seat you can increase power through the hind end, but a lot of the impulsion and power stuff is also through the back, so getting your horse to stretch through the neck and back could help :)
Pick his head up more and he can use is hind end better