I've never sailed on the Columbia R, but I was there last summer, and it looked like it would be a blast. Here is an image from about 22 mi further inland from the Bonneville Dam. That is Mt Hood in the background. Kite boarders were all over the place, but there were no AI/TIs out.
Every day the winds blow strongly UP
the gorge. I think you would have a strong tailwind every day, making it easy to go upriver
. I'm assuming that the opposing current would not be a major problem. Reversing the trip
, however, would mean tacking against strong winds. You might be able to go back down river simply by furling your sail and riding the current aided by as much pedaling as you would like to do.