When are you going to be in SEA? I'm planning on heading in for the weekend of 5 March.
Just tell them you're there for shopping.
The wait at the Peace Arch crossing can run into hours, but there's a "truck crossing" about 10km to the east that almost never has a wait. I think you can find the route through a search here. It isn't hard to find.
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-alan in sitges, home of the new, improved, and now
legendary Si-Re-Do