How do you teach your horse how to canter?

I have a young standard bred....ex harness racer...and he knows how to canter but i dont know to get him to canter...any suggestions?

Answer: 
I suggest you try in a practice ring. Start with a walk, then a trot. If you are going to the right, you look over the horses right shoulder, give a couple of taps with the LEFT heel, and a couple of "clicking sounds. He should canter, if he doesn't, stay with it until you accomplish what you want. This method also forces the horse to use the correct lead. If you are going to the left, you glance over the left shoulder, and give a couple of taps with your RIGHT heel. Remain calm, but determined. It should work. I assume you know to hold your reins in your left hand in a controlled manner.