I havent heard of things being xrayed when you go accross the border by car. They may search you if they think your suspicious though. And if they do try to xray, just ask them to handcheck the film.
xray machines, such as used in airports, can only truly potentially damage high speed film. i've been back and forth to europe, asia, etc. and have never had a problem.
when i say 'high speed', it is documented that xray machines 'may' damage 3200 speed film (box rated).