I've encountered problems going into both as one person, riding or driving alone, sleepy crossings or major. Sometimes I'm welcomed, sometimes it's a problem. Once when riding with a friend we split up before the border, he was a Canadian resident and I US and we were just being cautious. I've had problems coming home to the US and this was long before 9/11, partly because of my Canadian origins and having a bit of Canadian ID and some US ID also. Now I carry passports for both countries. They can still harass me but eventually have to let me in. Also on occasion I've been met with a welcome and a smile into both countries. I try to be respectful and courteous and have my papers ready. Look them in the eye, sunglasses off if possible, yes sir, yes ma'am. Now's not the time to show how you really feel.