For those considering rail, AmTrak is offering a bargain rate fare of $13.60 each way (no taxes) between Seattle and Vancouver during that period.
Unfortunately this applies only to the daily direct train service which irritatingly only departs Seattle early in the morning 7:45 am or so (usually forcing an overnight stay in Seattle) and gets back just before 10 pm which is too late except for a handful of redeyes. Getting to and from SEA and the Seattle rail station is not cheap if you are in a hurry.
http://reservations.amtrak.com/rs.html