Depends on when you plan on traveling. 0600-0900 or 1400-1900 through Portland the freeways become parking lots and you’re better off on the Santiam. The highway won’t have any weather delays this time of year but there are plenty of podunk towns with 30 mph speed limits on your route.
For Oregon ALWAYS check Tripcheck.com. It's the state's AWESOME road mad with all notices and restrictions. I even used it when on roads near OR border. It's especially important to check road conditions during fire season and snow season. When they close roads for fire/snow some of the alternatives are a PIA.
This time of year I would go 20 but like tscottme said check Tripcheck, there is construction somewhere past Burns and there could be things like clean up from fires, around Lyons and vicinity, just outside of Stayton. All, or most is 2 lane and more curvy but it's a nice drive, with you going though more small towns.
Back in Oregon headed to the dalles. Using oregons map I see us 197 is red around maupin. It just refers me to map 1 for legal length, not sure where that would be. But anyone know if this probably means us 197 is a no go to the dalles?