Hey Tapio, welcome to iFish! My brother-in-law is from PG; played hockey for the WinterHawks back in 1983 when they won the Memorial Cup. I've never been up there, but I've heard stories about the moose hunting and the fishing! His family all moved down to Kelona a few years ago to get away from the cold winters.
I'm not a big steelhead guy, and I'm just getting into fly fishing. Don't know that there are any salmon runs that time of the year; you might look at some of the other forums for that answer. You could spend a few hours using the iFish "Search" feature and probably learn a lot. There's a lot of great guys here, but the Fly Fishing forum doesn't get as much action as some of the other forums.
Generally, I don't know that there is a lot of fly fishing right around Seaside. The Necanicum follows Hwy 26 for a ways, but I've never fished it. If you go a little farther south to Nehalem Bay you could get onto the Nehalem, Foley Creek, and a number of nice streams. Farther south toward Tillamook you could get into the Wilson River and the Trask River.
There's a book called Fishing In Oregon that's pretty good for describing the fishing opportunities in different sections of the state. You can get it online from various sources.
Oh, the tradition here is that newbies have to offer up a hunting and fishing story so we all get to know ya' better. So, we'll look forward to reading that real soon!