The mapper at acme.com (http://mapper.acme.com/) is an excellent resource for comparing topographic maps and Google maps/aerials, but is there a similar site for Canada and Mexico?
I haven't found one, but I'd be interested to know as well.
Acme used to have Canadian topos but they disappeared a number of years ago. I was disappointed.
Well, if you'll accept low-res satellite in lieu of aerial: http://atlas.gc.ca/toporama/en/
If one had the time and the hard drive space, one could probably create one for Canada from existing public data. I've recently discovered that their digital elevation model is available online.
Canadian maps courtesy the Federal Government
http://atlas.gc.ca/toporama/en/index.html
There's also MyTopo http://www.mytopo.com/maps/index.cfm