Service adviser (repair place) said okay but we have a good relationship. I don't think they will give a formal letter on letter head saying "miles_navigator can take this car to Canada" and nor do I want to ask my service adviser to get such formal letter.

Repair place just gives generic form saying "miles_navigator can drive this car" (no specific mention of Canada) with VIN # and amount of gas I am supposed to bring it back with. If I wasn't crossing international border, I wouldn't even think to ask this question before taking it on a road trip.