Traveling across borders south of the border in your own vehicle always puts you at risk of having your vehicle seized by the authorities, also nice vehicles are magnets for criminals and corrupt cops looking for bribes.  I'm not saying I know the risks are high, but I recommend looking into them. 

An epic trip I have been daydreaming about is to do the entire Trans-Canadian highway over the summer, from Vancouver, BC to St Johns, Newfoundland.  I did most of it in two legs a few years ago, but petered out on the eastern leg before I got to Nova Scotia.  It's really amazing up there, in terms of incredibly hospitable people (outside the biggest cities, at least), wide open, immense spaces with almost no people at all, and just plain peacefulness.  I remember coming back to the states and being disgusted with how vicious and crowded the old normal seemed.  Just an idea...