Not Portland. Bellingham, Washington, about a mile from my house. Google Alaska Ferry.
The regular ferry runs to Haines and Skagway, not all the way up to Seward or Valdez. This needs to be taken into account, because Alaska is a big place. There are a few boats which go further. It's also worth knowing that even the regular, shorter route takes several days, and it's a fair bit of money. On the other hand, it's a good time in its own right, and you'll be riding on the return leg so you won't miss that much.
It's also possible to ride to the northern end of Vancouver Island, take the B.C. ferry to Prince Rupert, then switch over to the adjacent parking lot and pick up the Alaska ferry there. There's no advantage to this, however, and some time lost in the process.
Deck class has always worked for me: a whole little community forms on each trip.
Hope that helps.