Found a news article saying that, at least in Quebec, there are a certain number of shots they can sell (as opposed to those given for free to citizens). They say it runs $75-200 CAD. However, there's also talk of them following us down the antivax rabbit hole and restricting them to "vulnerable populations" this fall. If this happens, it might go on a province-by-province basis, so it might still be available in certain provinces.

Can't find anything concrete for Mexico, but I would say probably.

The US might also start refusing vaccinated people entry at the US border, since the vaccine can be contagious.