I had a car that I sold, and it was transported to Canada. It was not able to connect to the ATT network in Canada. When 5.8 firmware was released, Tesla called me many times concerned that this car that I no longer owned was not getting the 5,8 update. After many calls, Tesla enabled this car to receive 5.8 by enabeling it to receive in Canada.
My best guess is that your Canadian car will not be able to be connected while in the US, unless Tesla enables it to the US network. Hope this helps!