It's been many years since I've ridden out in the gorge for any extent.

I-84 has lot's of traffic and back then, was fairly doable (at least the section I typically rode from Cascade Locks back in toward Portland). Much depends on the debris and such. The one really uneasy section was at Bonneville Dam, that on-ramp crossing and shoulder seemed narrower than other sections.

Old Hwy can definitely be unnerving due to minimal to no shoulders and all the summer tourist traffic including motorhomes. Take the lane when riding and if it looks like it is backing up, there are a few spots to pull off and let 'em by.

US26 has some pretty good, wide shoulders for the most part, been a while though since I have been up there and even longer since I have ridden up there. It's good if you are looking for a climbing ride though and it is certainly a lot of fun coming back down. I don't remember what the section around Zigzag looks like shoulder wise. I do see cyclists riding up there though.

Another route for distance I did way back was to ride out the Washington side (fair to medium shoulders) to Cascade Locks and back on I-84. That saved doing an out and back on I-84, and the Washington side is pretty scenic as you go up and down along their cliff sections.