So if I live in the U.S. and am a U.S. citizen, drive to Canada (using passport to cross), then fly out of Canada to Europe the same way, is there any law I'm breaking? I can't believe I'm asking this, but these days you never know, and the last time I left the country was 2006.

For instance, if I drive to Montreal, stay for a day or two, fly Montreal to London, stay for a week, and return the same way - any major issues with getting back into the U.S. driving across the border?

exbayern, just saw your post above mine (it posted while I was writing). Will check for other threads.