Work back to front, leg to hand to get a good balanced canter.
Canter poles work wonders
transitions to get your horse listening to your leg so when you canter the horse will be able to listen when you want to either collect or extend
Many transitions on a circle from 4 steps trot 8 steps canter and so on
Once you have a nice trot and nice transitions, canter poles are excellent for getting your horse to pick up their feet, lift their back, and think about what they're doing.
You have to work actively in walk and trot first to get your canter be controllable, smooth and in good rhythm.