Whats the best,easiest and or cheapest way to get from Vancouver to Seattle?

We are cruising from Seward to Vancouver in early July. Airfare from Vancouver to Philadelphia is $770 or so for each of us. Air from Seatlle will be $200 each (possible lower). So we decided to drive into Seattle if thats a decent option. Then I heard about a train connecting the 2 cities. Does anyone know of this train? Does it exist? Is it safe, comfortable, reliable? How can I find more about it?