Sigh... this persistent lie that huge numbers of Canadians run to the USA for healthcare is just that, a lie. It's been studied many times. Here's the abstract from one paper:
...Results from these sources do not support the widespread perception that Canadian residents seek care extensively in the United States. Indeed, the numbers found are so small as to be barely detectible relative to the use of care by Canadians at home.
Here's another from the popular press:
No, Canadians do not flee en masse for US health care
All the actual research
on this consistently shows that Canadians are not
using the US healthcare system in any substantial way.