Driving up west coast, California North

I can't speak for Califonia but you'll love Oregon Coast Now if I were driving, I would avoid Portland and Seattle completely but I just hate the traffic so I would head up the WA coast and if you want to do the 101 loop, going up along the coast and then back down along the Sound. You could take Hwy 3 to Tacoma and deal with the Narrows Bridge ($$) or just keep going around to Olympia and hook up with I5 there. Continue past Fort Lewis and turn off I 5 on Hwy 512 Puyallup, and continue to Hwy 167 Seattle (Not Tacoma) and in Auburn take Hwy 18 to I90
But if traffic doesn't bother you and you really want to see something more than and Interstate, take Hwy 12, or Hwy 2 over the Cascades.