It’s been years since I’ve crossed the Canada/USA border, so things may be different today. But when I went, the Canada side was more concerned about smuggled weapons, while the USA side was more concerned about smuggled drugs.

Apparently if you go from New Brunswick in the morning, spend the day driving through Maine/New Hampshire/Vermont, and cross into Quebec the next day, that’s suspicious enough to get detained for several hours and to have your entire car searched at the border. To me it just made sense to do a straight line drive through those states, since staying inside Canada between those two points would have been a much longer, more convoluted route. Silly me, being logical about my route without considering how others break international law.