flyhighdude,
Light planes, particularly float planes, flit backwards and forwards across the border between Washington and BC all the time.
Besides all the good advice given above, there is bound to be good local knowledge at the location you fly from in the Seattle area.
I've crossed four times between Alberta and Montana and one of the really important things is getting a discrete transponder code before you cross the border.
I'm not sure how that requirement is applied to the Washington/BC border. In 2016, I got a backseat ride in a Nanchang formation over the Victoria Cenotaph on Remembrance Day. I was quite surprised to see that we maneuvered over the US San Juan Islands on the run-in, while under control of Victoria Approach.
Also, the direct VFR route from Vancouver to Victoria cuts through US airspace on the way.