OTOH, this summer while crossing the canadian border in Madawaska (ME) to enter the US, I was "stopped".

For some reason the US immigration officier in Puerto Rico had forgotten to add a date to my entry stamp. I was stopped for this technicality, and while getting some paperwork for me in my car the custom officers found I had prescription drugs.

I was worried, but for no reason at all - they figured out the mistake that happened in PR, and checked the drugs official prescriptions matched (antibiotics and some pretty stong painkillers), and then I was cleared to go with a smile.

TL;DR : the US custom officer were friendly and efficient, and fixed a mistake.

I wouldn't dream of that happening in Europe, or (god help me) the UK.