Hold on here:
Why would an American assume that Canadian medical providers would "accept" their US insurance? The docs generally don't have a way to bill the insurance, nor would any hospital except one seeing loads of US people.
The best you can expect is that your insurance will reimburse you for your medical expenses. Meanwhile, that doc and hospital wants to be paid, just like anyone else.
If someone is concerned about that, I suggest they purchase medical evacuation insurance, such as MedJet, and be brought back home.