Heading to Montreal was a breeze. There were only 2 cars ahead of us and they didn't ask to search the car. Just a couple of quick questions and off we went. Total time = 10 minutes.
Getting back into the US? Completely different experience. Extraordinary traffic and I happened to choose the line that refused to move. Wait time to get to the border agent = over an hour.
Once we got to the booth, we went through quickly. Again - no search required, but we were asked to roll down our back windows for a peek. No idea why it took so long but it was a Sunday afternoon. I might go back to the smaller border crossings in the future (this was my first time at the big one).
I recommend parking and hitting the restrooms (which were disgusting, btw) prior to getting in line. They're right at the entrance of the duty free building. I did see people getting out of cars and walking to the building to use the bathroom since the wait was so long.
Might as well peruse the duty free shops. If booze, perfumes and funky candies are your thing, ya might as well drop a few bucks here. You can use Canadian and US dollars combined; great way to shed any extra paper money.