I have had to visit medical facilities twice in British Columbia while cruising. Once to a medical clinic for high blood pressure, and once to an ER for a similar problem. Both times I was treated and not charged anything at the time. When I later received the bill, it was reasonable and below the deductible for an out of network doctor. As I recall the ER bill was $144 for a 2 hour visit, complete with tests.
I have heard that if you are on medicare and need medical help in Canada, to say that you were in transit thru Canada to another part of the USA. Otherwise mecicare won't pay.
When we stayed near Victoria BC, we would take the boat out into the Strait of Juan de Fuca a couple of miles and connect with a Sprint cell tower in Port Angeles.
For near border operation, I think calling the provider in advance to advise that you are near, but not in Canada is a good idea.