Getting from the border back to Seattle is easy. From Manning Park Lodge, the Greyhound comes by and will take you to Vancouver (about 3 hours). Either stay the night in Vancouver (I’d leave the bus station area and head toward downtown, spending some time in Chinatown along the way) or get on another Greyhound bus to Seattle (about 4-5 hours). Make sure you have a passport.
To get to the PCT, well, it depends on where you want to start the PCT. For example, getting to Snoqualmie Pass (about 250 miles, and all quality) is pretty easy: Put out an email to the PCT-L. There are lots of former thruhikers, section hikers, and arm chair hikers that live in the area and will give you a ride. If I’m around, I will, but I’ll probably be hiking. Seattle to Snoqualmie Pass is less than an hour, so it is pretty easy.
Starting at White Pass doesn’t get you a whole lot more. It adds 100 miles of mostly pretty boring terrain, though with a few highlights around the Rainier area. Also, much clear cutting. People that live in the Tacoma-Olympia area could easily drive you there, though.
If you want to start at Cascade Locks, it would be better to fly or bus into Portland and get a ride from there. There are a bunch of hikers there that monitor the PCT-L and they’ll give you a ride. It is only about an hour, if that, to Cascade Locks.
You can sign up for the PCT-L at http://www.backcountry.net
Suge