I think you are making a rather liberal interpration. There is no "unless" on the end of the Ontario regulation. If it is a portable toilet, it is illegal in Ontario. Probably okay in the rest of Canada though. I am glad that isn't somewhere I sail, though a "someday" Summer trip is a possibility. My boat actually has a spot for the bucket molded into the hull; you can't just take it out and drop a head with a tank in.
Newport 17 - "Kohanna"
At sea Darwin's hypotheses is the final arbiter of right of way.