The dumb thing is...as Canadians, we can't purchase travel/health insurance after we've crossed the border into the States. It HAS to be taken care of before crossing the border. But an American can go to any insurance agency (or through Blue Cross) & purchase travel insurance for the duration of their stay even AFTER they've been here up to 5 days.

Here's a quote from the Blue Cross website:

For visitors to Canada, emergency medical expenses can be overwhelming. Blue Cross Visitors to Canada Travel Insurance is a necessity. So relax and enjoy your stay in Canada. Please contact a Blue Cross Member Plan either prior to or within five days of your arrival to activate this coverage.

Mrs. Dirtfarmer