Not trying to be picky, but it is Calais, not Carais. It is pronounced Cal- iss. (Rhymes with malice). I advise you to take the new border crossing, not the old one where you have to go through the town and cross a small bridge. When you get a few miles before Calais, you will come to a traffic circle. Take it 3/4 around and there is also,a sign there that says border crossing. That leads to the new one. If you go straight ahead you will come to the town and the old crossing. No big deal either way, just easier.
We have crossed a number of times in the last few years at different border crossings and git is easy. They didn't seem super fussy about food, but be honest. Most you can lose is a few bits of produce.
Get fuel at the Irvings in the U.S. Just before the stop sign and right turn at route 9, I believe.
Nice campground on the water in .st. Andrews