As stated earlier, if you are traveling with your passport one alternative to continuing westbound from the Northern Tier route, you can go north and ride across Canada to Vancouver. A couple of cyclists came through the office today and recommended this routing from their experience:
From Tonasket, ride US 97 north to Oroville. Then northwest on Loomis-Oroville Rd along the Similkameen River for 21 mi.
Then leave the river to continue north to the border crossing where the Loomis Oroville Rd. turns south. (The border crossing has limited hours, see this website for more information http://www.ezbordercrossing.com/list-of-border-crossings/washington-state/nighthawk-chopaka/#.U9KoeIBdWQ0
Continue north on Similkameen Rd. to Crowsnest Hwy./PR 3.
Ride PR 3 north to Hope, then west on Lougheed Hwy./PR 7 to Vancouver.
As you enter Vancouver route will become Broadway St. As Broadway St. gets busier you can go south 2 blocks to 10th St. which is the bike route into the city.