All except for Salem...
I agree with Lynne. The given route looks pretty good. The only part I haven't ridden on is the stretch from Hopewell southwards. It looks like a pretty annoying stretch as you go through Salem.
The issue is crossing the Willamette. I think I would probably opt for crossing the Wheatland Ferry (head east from Hopewell), go through Brooks and the Labish Flats (65th & 62nd) to Hazelgreen, then Howell Prairie Road.
In this manner you would avoid Salem altogether, since your stated end is to drop down towards Detroit anyway...
ORS 811.065 (1)(a)
The driver of a motor vehicle may only pass a person operating a bicycle by driving to the left of the bicycle at a safe distance and returning to the lane of travel once the motor vehicle is safely clear of the overtaken bicycle. For the purposes of this paragraph, a “safe distance” means a distance that is sufficient to prevent contact with the person operating the bicycle if the person were to fall into the driver’s lane of traffic....
LCI #2105 Lambchop Rides!