Start to bump him and make him relax more.
If he gets out of hand half halt and get his attention
Soft seat, lots of leg to encourage the horse to move onto the bit and accept your contact, and hald halts on your outside rein. Reward with give when your horse slows, don't hang on his mouth as he'll likely just get faster to try and run away from the pressure. Good luck! Hope I could help <3
Give small bumps with your hands and sit back.
Give him pulses with your hands. Pull release, pull release. Also make your seat as soft as possible
When you want him to slow his canter pull on the reins and squeeze with your legs, it tells him to slow down but also move on at a slower pace.
If your horse rushes in the canter, do lots of circles and turns to help him improve his balance and slow him down, since unbalanced horses rush in order to steady themselves. Circling engages their hind end and makes them put their back legs underneath them to steady themselves.
If he won't slow down in the canter, despite you giving him clear instruction to, maybe a change of bit will help (try and avoid using a stronger bit - this will make the situation worse). Horses that don't like the bit tend to rush away from your hand in an attempt to escape from the discomfort in his mouth. It also helps to have a different cue to slow, such as 'woah' or shifting your weight back in your saddle, rather than relying on the bit to slow your horse.
Finally, lots of transitions from trot to canter help a bunch as this gets him listening to you more and he will eventually slow when you ask.