Bruce, neither side of the Columbia will be 'tranquil' while you're on the main road/highway. Both though are beautiful and scenic. The Washington side becomes more quiet the further east you are and more crowded the closer you get to Portland.

I've not ridden on either road but have driven both many times and always do a 'note to self' to do a ride there.

One thing you may consider, depending on the amount of time you have would be to go out the Gorge from Portland, cross the river at Biggs, ride the Washington side to Hwy 221 then up through Horse Heaven Hill and into Prosser, the heart of Washington's wine country. Spend a day or three riding the backroads btween Benton City and Zillah, visiting wineries and breweries. Lotsa places to stay/eat/see. Then back over Hwy 97 and back down to the river and into the Portland area.

If I can do anything for you, let me know.

Dave Thompson