One hears about the Bethany ponds. I have never bothered with them. And I avoid Beaverton almost as much as I avoid Portland, on principle.
There are a few canoe/kayak ramps on the Tualatin out in the country where you would find at least as good bank access as at Cook Park, and probably fewer people there. The new park at River Rd. and Farmington, the 99w bridge overpass just south of King City, and Rood Bridge Park in Hillsboro come to mind. The Tualatin is a snaggy river, of course, so adjust your gear and approach accordingly.
By that I mean don't plan on dropping plastics or running Texas/Carolina rigs on the bottom. Pulling a spinner and keeping it shallow will work until you find the snags. Run a bobber with a drop shot below to keep things shallow. Run topwater plugs etc.