As a professional Divemaster I can tell you face-blank, Canadians are horrible tippers. Period. But, most of them are so happy go get out of that cold Winter for a while and go warm-water diving, that they make up for it with friendliness and ease.
Most DMs do it for the free diving, and tips enter into it as gravy (this is for daytrip DMs, not liveaboard DMs, and certainly not Instructor slaves). Also, I learned long-ago, that if I were to make a living at DMing, I would have to own the dive-guide business myself; the right way to do it.