I'm a longtime walker/hiker in the Portland area, Columbia Gorge, Newberg (lived 8 miles from Newberg until last December).
I also find the timeline to be a problem. I'd never consider getting from PDX to Newberg to Cascade Locks and back to Portland in 5 hours. But, it's a raaaaaaccccce! At least a noon arrival at PDX means they won't hit traffic.
Champoeg State Park is just across the Willamette River from Newberg, via a bridge. They have lots of tall trees there. I used the forested path from Butteville into the park as my main marathon walk training route for over five years. Yep, those could be the trees. I know them intimately. Also, there are still plenty of big trees just outside of Newberg on the hills. I've done walks the past 2 years that started at a winery and went through forest on the vineyard grounds. We are not deforested completely around Newberg. (FWIW, I wouldn't drive through Newberg to get to Champoeg, I'd stay on I-5 and cut over through Butteville, much faster, but I'm a local). Actually, Champoeg has an address in "St. Paul" rather than Newberg, so the climbing might be on private land owned by a farmer or in the hills around Newberg.
Cascade Locks: the Columbia River around Cascade Locks is NOT A LAKE. Yes, it is an impoundment behind gigantic Bonneville Dam, but there is a current around Thunder Island and can be a lot of chop and waves in the water when the wind is blowing. And the wind blows 99% of the time, HARD. Cascade Locks is a very windy place, and this area is frequented by sailboarder and windsurfers as a mecca. There can often be whitecaps on the river from the wind chop around Thunder Island.
I can't see the clips yet to comment on Columbia River vs. Willamette River. The Willamette River at Champoeg isn't very swift and it's far, far, far narrower than the Columbia at Cascade Locks. May is the high run-off season, so either river would be high. Bonneville Dam would be spilling the excess, so there would be a good current at Cascade Locks.
I've strolled around Thunder Island on volksmarch walks at least six times, I know it well. Lots of geese doo-doo. It is a popular wedding venue, although you definitely risk losing any hats or veils. Last June when I went over the little bridge onto the island, I had my hat secured around my wrist and it still blew away and I had to chase it.
Bridge of the Gods is a very scary bridge. We had one volksmarch that crossed it. It is open steel grating underfoot for most of its length. Total vertigo experience. It is a looooooooooonnnnnnnggggg way from Bridge of the Gods to Thunder Island, so I definitely believe the 2000-ft zip line! The Pacific Crest Trail crosses the bridge and those who are using pack animals have to blindfold their horses to lead them across. I don't know if they do any other physical tasks, but the trails up from Bridge of the Gods are gorgeous but steep, a real hike.