Canadians do not have a 'right' to enter the US, just like Americans don't have a 'right' to enter Canada.
When you enter another Country you are in fact a 'guest' in their house and must follow their laws and customs. A person or a country can make a decision at any time to limit the guests or the numbers of guests coming into their house, its their right to do so.
The US could easily decide to do this. Look at what the Europeans within the EU have done to us and the Americans starting next year -
Official EU website on ETIAS, the new travel authorisation for visa-exempt travellers to enter 30 European countries. Applications should be filled in this website from mid-2025.
travel-europe.europa.eu
This could easily, easily be applied here by the Americans to us.