The problem with Canada's bullet points is that it's not obvious that you need it for a cruise departing from Canada. As written it reads as if you only need it if you have a port stop is Canada
The benefit of a travel agent isn't in booking the cruise, but managing all the issues that could come up (and in the covid era, they come up) after booking.
Yes. There's no rule that says you have to get off at any port. There are plenty of frequent cruisers that never get off the ship for anything other than getting a bag of coffee or something in a given port.
So some extremely disgruntled former owners are doing their best to show their frustrations and seem to have some government allies in the process.
That'd be a quick cease and desist order in the US