My Amtrak trip to Canada was part of a trip around the country (http://www.snugharbor.com/~lwood/trainabout/) on the coolest damn rail pass (http://www.amtrak.com/savings/northeast/promo-passintro.html). I wasn't asked for any proof I didn't intend to stay in Canada, I just turned up at Penn unghodly early to board the Maple Leaf, and showed my passport (which is unneccessarily overkill; a driver's license and SS card or birth cert will do).

When lori and I went by car on I-5 (north from Seattle to Vancouver), it was painless as a toll booth: we just pulled up to the booth, they asked for some ID, and waved us through.

American Customs were, in both cases, more annoying than Canadian.

-- Lorrie