Oh man, Seattle is probably my favorite city -- I would go visit anytime I could.
If you're driving in from Vancouver, stop by Seattle Premium Outlets on your way down I-5 if you're into shopping. It's also next to a Wal-mart Superstore which is a tourist attraction of its own
Pike Place Market is pretty cool (flower bouquets are wicked cheap -- good way to impress the GF!); I also want to go see a Mariners game if I go back this summer (we went to a Seahawks game last year and it was pretty awesome).
No suggestions on a hotel, although I would suggest staying outside of downtown if you have a car and you're trying to save costs. Have fun!