Well here's how it goes: First, it's not a national law, it's a provincial one (a province is very much like a state, really). And the province does not regulate that people must wear masks, because that would be against the Charter of Rights and Liberties. So instead, they force the CORPORATIONS, which have no rights or liberties, to require people (their customers) to wear masks.

As such, it's a private entity (the corporation) that has a "private" rule on access to the premises. But they are liable for large sums if they don't enforce the rule, and they can call the cops on anybody not wearing a mask as a form of public endangerment. And of course those fucking thugs can feel like they need to beat you up if you hesitate to comply.

The ONLY recognized reasons to not wear a mask in my province are: 1, if your face is so deformed that a mask won't fit. 2, if you are severely mentally handicapped and can't understand the reason why you are forced to wear a mask and you take it off. THAT'S IT.