Seattle is not the most traffic friendly place. I-5 either around Portland north. I stay as far away from I-5 as I can so I can enjoy this beautiful country. All freeways for that mater.
395 goes to John Day.The John Day fairgrounds is a good place to stay and ride around the area. The NE corner of Oregon caters to motorcycles. The roads are great. I have ridden over there for many Memorial Weekend riding. I have extended my rides over there to a week before I got our 380TH. I took it and the bike over there for a week a few years ago. I never get tired of all the riding. Scenery is great too.
Mt Rainier NP and Mt St Helen are sights to see in Washington. Leavenworth, Wa. too.