The best way to get from Seattle to Vancouver BC is by way of the Amtrak Cascades train. It takes about the same amount of time as driving, costs less when calculating the actual cost of driving (a tad over 50 cents per mile according to the IRS and AAA) and is much more comfortable. An added bonus in my opinion is that you feel like you went somewhere if you take the train. When I drive to Vancouver it feels like I went to Spokane or Portland. The train adds to the experience.