Since anecdotes are so effective in the debate about health care...
A aunt and uncle of mine had an apartment in Florida that they would go to each winter, much like many senior Canadians do. One year my uncle experienced his first heart attack, and went into a US hospital. Even though they had Blue Cross coverage, the medical bills upon release were still quite large.
A few years later, they had just left the apartment to come home to Ontario. He started to feel tightness in his chest, and knew another heart attack was imminent. Rather then stop and check in to a hospital in the US, he drove through the night from Florida to Ontario and checked into the first hospital they found on arrival. Fortunately he had the heart attack in the hospital in Ontario and he was OK. Better yet, the bills were negligible. He wife was with him the whole time, she condoned and supported this decision (and no she didn't have a drivers license). They knew they couldn't afford another stay in a US hospital.
I think this is why I'm so leery of traveling to the US. If something goes wrong, I'll be damned near broke. Normally I'm not a glass-half-empty kind of person. But this story has stuck with me through the years.