Grew up in Olympia, now residing in Tigard (just south of Portland). Rabid Hawks fan since team inception.
Portlanders in general have no issues with Seattle that I've heard of since living here. The only ones who have the "little brother" syndrome are the people who "represent" Portland, ie: the local ESPN radio station.
Unless I've been going to the wrong places, Portland isn't a very good pro football town. They love their Blazers, are divided with Duck and Beaver fans, and I do see a lot of Hawk gear, but overall not real hot on pro football.
Now, the Timbers are another matter. Evidently soccer is the official sport of hippes and rabid liberals everywhere.