Hey travelbro. I went from Vancouver to Arizona last year with the gf. I wouldn't worry about car stuff at all, just make sure you buy some travel and medical insurance for the states cause you can get really fucked with their healthcare.
I wouldn't worry about the car, we have a 06 civic and it went great.
I'm going to project a little about you as a fellow (ex)-Torontonian and give you a piece of advice which I wish someone told me earlier... Go to the National Parks. Spend 2-3 days along your routes to see the raw beauty in America. Nothing... and I mean nothing else you'll see will leave such a lasting impact on your psyche like the 3000 ft walls of Zion, the view from a summit in Tetons or the Rocky Mountains, or your own miniscule scale standing in the Grand Canyon. Don't just be a typical uninspired tourist there and go on the pavement-herded trails. In each park find a small obscure corner and explore it, actually be there, present in the moment.
It's fun to stop by the small towns along the way when they have a fun character but most of those things are superficial tourist traps. You pay $19.99 for your 'TOWN THEME TRINKET" and have a 10 second anecdote for your friends about how it was.
Finally, get your priorities straight and see Canada's parks (although this year sucks cause they're overloaded).