You have several options. there will be a cruise contracted bus, independent shuttle via Quick shuttle, one way rental car- I have rented from Avis, Budget and National, also look at Hertz. You want a DOWNTOWN Vancouver pick up and Seatac drop off if you need the Seattle airport. Then there is also the train leaves Vancouver around 6pm, rest of runs are via buses. Need a cab from downtown Seattle to airport about $25+.