Thanks for the suggestion(s) cdumitru. I tried the Columbia near the Warrior Point parking lot today, as you suggested, and had 45 minutes of good action (hooked 3, landed 1) right away followed by about an hour with only one bite & no hookups. Still it was a promising spot, definitely deep and fast out there!
I wish I had more advice for you concerning the channel cats on Sauvie, maybe someone else here has more tips. But I've only caught them between Big Eddy and Sturgeon lake, so the highest stretch of the river. There are periods where I and/or the people around me can't keep them off the hook fishing worms on that stretch of river. So far I haven't seen one out there over 12 or 13 inches yet though. And I haven't hooked any, or seen any hooked, below Big Eddy, tho I'm sure they're there...