[pct-l] Getting to Manning Park for a southbound start

[Tom Rogers" <tom-rogers@home.com (Tom Rogers)]

I'm planning a southbound hike from Canada starting in late July.  The guide
wasn't very helpful on a few issues associated with getting to the starting
point and crossing the border.  Specifically,

 What's the best driving route from the Seattle area (someone is driving me
to the trailhead and returning)?  The guide mentions stopping in Sumas to
get pre-inspected by US Immigration, is this necessary, or advised (does
anyone care)?