My boy is 18 hands and is a bit clumsy at the canter so we don't really canter much. Not much need too. The gaits are really smooth. He has a really long stretch with those legs.
You do have to be careful coming up behind other horses because the pounding on the ground gets some of them spooked.
How old is the horse you are buying? It took awhile to get to the canter stage. I didn't ride until well after he turned four though.