The Quick Shuttle bus is the easiest option. US$35 o/w Sea-Tac to Vancouver (the fare in C$ is lower). 8 departures daily.
www.quickcoach.com

Amtrak's Cascade service leaves Seattle annoyingly early at 0745. Later services are bus or train to Bellingham and bus the rest of the way. Airport<==> Seattle rail station by shuttle is about $8 or so (I just posted this to rec.travel.usa-canada and rec.travel.air earlier this week). There is a bus option if you have time. Amtrak apparently earns AS miles.
http://www.wsdot.wa.gov/pubtran/casc...mtrakcascades/

As for ANC-SEA, check with the cruise line to see if they have one-way tickets back down as there are pax flying up for the cruise back down. Otherwise check www.AA.com and www.Alaskaair.com They are the only 2 games in town.