Actually, Canadian (and British) postage stamps used as revenue stamps are very common. Unlike with U.S. stamps, such use wasn't expressly prohibited.
It's the U.S. prohibition against using revenue stamps as postage and vice versa that makes them more scarce and collectible.
Still, even if the Canadian & Britsh equivalents are not overly valuable, they still can be fun to collect from an aesthetic perspective.
One of my favorites is the one below. What you can't see from the scan is that the circle around the ship and the rays eminating from it are printed in metallic gold.