You've already gotten some good advice about the cantering issue. I'll just throw in, since you mentioned about moving up to BN, the dressage test is usually the same. If jumping is his stronger suit, there's no reason to not move up.
Also, in case nobody said it already, a good canter comes from a good trot. Trot improves balance, so if you consistently have a good trot, it should slowly translate into more fluid canter transitions and he figures out which leg does what.
You just have to see your distance...you don't have to like it.