I think you could spend a month in both Oregon and Washington and still not see everything.
You may not know this, but Washington has the only rain forest in the USA, one of the highest mountains and is 2/3rds desert. Add to that the Coast, Puget Sound, too many State and National Forests to count and Washington alone will keep you busy for a long time.
The West side of Both Oregon and Washington are green and wet, wetter the farther North you go. The East/Central side are dry and desert type of landscape. All of this is divided by the Cascade Mountains. Countless lakes, rivers, forests, gorges, and mountains are all through the area.
The list of things to do outside the cities is near endless.
As for cities, Oregon has Portland and Eugene for its 2 largest cities. Portland is very interesting, and eclectic, hippy vibe, etc. Tons of restaurants and cool shops to visit, but the traffic will drive you crazy. The East side has Bend and it is a cool tourist town with lots of fun things to do. Skiing, rafting, Mountain biking, etc.
Washington of course has Seattle with so many things to see and do. Olympia is smaller, but also interesting. Skip Tacoma, it does not have much to offer other than crime and a very bad smell.
Keep in mind that the traffic from Olympia to North of Everett is some of the worst in the entire country. There are only 2 major roads I-5 and Hwy 167/I-405 that take you through the extremely densely populated area. Pack you patience if you travel through the Seattle/Olympia area.
Once East of the Cascade Mountains the traffic is near zero. Only Bend and Spokane will give you any issues at all.
Don't forget about Idaho, it also offers some spectacular sites to see and is worth visiting some time also.
A big thing to know is, do you want to stay on road and see cities, tourist areas, or do some off roading and get away from the cities.
As you can see, to give you any real advice, you would need to tell us when, how long, and what you want to see. Unless you have a year, you just will not see everything. I have lived in the NW since 1980 when I moved up from Cali. There are still things I have not seen and I travel a lot.