For how long can you go and what month? From what I understand, Mt. Ranier NP and presumably Whistler are best in late July/early August, when the snowpack is at minimum and wildflowers are at peak. If you're going earlier, you might want to prioritize the beaches and coastal forests.
I'd probably prioritize Olympic National Park above all else. As they say, it's like three parks in one -- rainforests, mountains, and coast. The variety is pretty incredible, so you can see a lot in a shorter period of time then say, hitting Cannon Beach for the coast and Mt Rainer for the mountains.
There are tough choices to make because there's probably 6 weeks worth of stuff to see. Roughly from south to north:
Southern Oregon Coast (Bandon Beach area)
Crater Lake NP
Northern Oregon Coast (Cannon Beach area)
Portland
Columbia River Gorge
Mt Hood
Seattle
Mt Rainer NP
Olympic National Park
San Juan Islands
Victoria BC
Vancouver
Whistler
Pacific Rim NP
A few years ago I did a 2 week driving trip from San Francisco (1 day)->California Redwoods (2 day)->Oregon Coast (3 days)->Portland/Columbia River Gorge(2 days)->Olympic National Park (4 days)->Seattle (1 day). It was awesome. If I had to cut it to one week I'd probably do Portland/Gorge (2 days)->Olympic NP (4 days)->Seattle (1 or 2 days).