Lunging Question? Should I Yank?

You'll just have to keep him in the canter until he relaxes. It may take a while though! Try to leave him alone while he's cantering. Don't pick on him just let him find that comfortable canter again. He'll pick it up, just make sure to keep him in the canter. He won't get it if you let him drop back down into the trot. So, only "pick on him" if he slows to the trot. Hope that helps!