You can buy local insurance at most Mexican border towns, I did if I was driving more than a couple of miles over the border (I lived at Lukeville, Arizona one winter and went to Sonoyta every day or two).

Canada is like an extension of the northern states as far as driving there. No problem. Language is less likely to be a difficulty. But any time there are international boundaries involved, there are risks as far as confiscation.

Now if you could just get the car rental folks to enforce their own no smoking in the cars rules. Last one I rented gave me a sinus headache the whole time I had to drive it.

SRS