I too am travelling to the Pacific Northwest for the first time this year...
Have some competitions in both OR and WA... and will take the opportunity to tour the Boeing factory while I'm there! (Cool!

)
I haven't travelled that route in particular.. but I have travelled elsewhere in the USA with AMTRAK and I think it's a good option when not in a tearing hurry..
The train you'd be looking at is the "Coast Starlight" from Oakland to Seattle...
Coach fare is USD $92... or USD$250 for a Sleeper (which includes meals) .. (I looked at 12 Oct)
As it is a 23 hr trip I know what I'd do!!:mrgreen: The Coach seats are however broad, and the pitch is generous to say the least!!!
That route is operated by the "Superliner" so you have a choice of upper or lower deck accommodation... No ensuites in the normal "bedrooms" but the (shared) showers are fine IMO...
Sleeper compartments on US trains are just big enough for the bunks (when folded down) but are comfortable enough night and day The bunks are not terribly large which is interesting given that Americans are in general bigger folks!... The US trackage is not as smooth as here IME so the ride is a little bumpy... YMMV...
As I just looove train travel none of these little things worry me overly.. IME the food in the Dining car is pretty good.....:mrgreen:
A whole bunch of airlines offer fares back from SEA to SFO for about $80.. so train one way, fly the other?
Hell... If I didn't already have time constraints/flights booked I reckon I'd have talked myself in to doing the train trip! :!: