I was on a bus over from Montreal, we were all in a big room after they had emptied the bus. One guy was born in Cuba and was Canadian now. The border guard asked him how he got to Canada? The guy says 'What do you mean?', and the border guard replies, 'How did you get to Canada, did you swim over?' Another guy had gotten a DUI in '79 in Canada, and the Guard was asking him about it in front of everyone. No joke, these guys may be doing their job, but they are a bunch of assholes, even to US citizens, and they are outside the law - you can be detained indefinitely at a border crossing without any probable cause, US citizen or not.