Politicians generally don't canvass much themselves at the higher levels.  Too much potential for nasty voters on the opposite side saying nasty, and turning it into a big press moment.  Obama does canvassing himself now and then, but that's all I've seen, and it's more of a photo-op thing than anything, I'm guessing.

Plus, he can generally get tens of thousands of people to show up to rallies, so canvassing would be an inefficient use of his time.  It might be good for McCain, since no one shows up to his events.

Be nice to America. Or we'll bring democracy to your country.