I believe the answer is no for tandems on Amtrak.
From the site: Recumbent, tandem and special bicycles over the standard bicycle dimensions and will not fit in a standard bicycle box are prohibited.
So if you can somehow fit your tandem into the Amtrak bike box, dimensions of 70" x 41" x 8.5", you'll be fine. If not, you're out of luck.
Someone could prove me wrong, but I highly doubt that Greyhound would be any better in regards to a tandem, and the same goes with airlines. You'd probably need a freight service to ship it to Vancouver, which, assuming you are based in the States, would be very expensive.
Hopefully someone who has toured with a tandem can chime in with some advice.
Another thing to note: Hwy 1 starts in Legget, CA, about 200 miles north of San Francisco. In WA, OR, and the rest of northern CA you'll primarily be riding on US 101.