I am Canadian citizen and for two years I was traveling every second week to US on TN visa. In all that time I got 1 "bad" experience from US side and 2 from Canadian side. (it wasn't that bad just longer questioning with 'trick' questions) Question which confused me a most entering Canada was "How long you plan to stay ?" , WTF , I have Canadian passport ? It took me a moment not to say "Not your damn business." and just play nice.... But in general crossing border is 99% no issue