Originally Posted by cyberdad

I wouldn't go so far as using the word "ignorant", but increasingly anyone without a passport is ill-suited for land or sea travel between the U.S. and Canada. Fortunately or unfortunately, the days of possibly getting by with nothing more than a drivers' licence are over.

I personally think the passport requirement for return from Canada is a bit extreme. But the fact is a passport is probably the easiest and most accurate way to provide proof of citizenship.