Upvote:2
Renting a car, if you are also returning to Seattle later. You can pre-clear driving across the border with the rental car company. Rome2rio.com shows public transportation options not one of which is late enough in the day. There is a flight on Delta Airlines that leaves SEA at 7:40 and arrives 8:38, which would get you into downtown Vancouver just a few minutes late.
(I assume you mean Vancouver, British Columbia, Canada. There is also a Vancouver, Washington, which is just north of Portland, Oregon. You probably need a rental car for that, too, but there would be no need to get approval for leaving the USA.)