When Americans think about Canada—and that doesn't happen often—they usually think of us as the nice, predictable guy next door who never plays his stereo too loud. Even Rob Ford, Toronto's ranting, crack-smoking mayor, has barely dented our squeaky-clean image.

But Americans shouldn't just think more about Canada. They should consider building on the two countries' free-trade deal and forming a more perfect North American union. It is past time for the U.S. and Canada to eliminate their border—either by creating a customs...