Originally Posted by
ohmark
I don't know about the bus and, of course, this thread is about the train.
Well, 80% of Amtrak Cascades operations into/out of Vancouver is actually on buses; for them, the border crossing is done at the actual border, in acceptable but boring facilities, instead of at Pacific Central Station. (So, if you do book on Amtrak, you might want to double check whether it's a bus or train that you'll be boarding.)
And while it may be "pretentious" (perhaps you meant presumptuous?) to assume you'd traveled outside North America, even before the impending passport requirement it's still very smart for anyone traveling cross-border to have a passport.