Just getting from Santa Rosa to Klamath Falls will take the greater part of a day. If you really get an early start and push it, you might get to Bend for the first night. Bend to Portland by any route we might suggest takes up day 2. Then, as I understand it, you have one day to get back to Santa Rosa from Portland (most likely, down I-5). I don't see when you'd have time to do anything along the way other than look out your windshield.
The only really scenic portion of the trip would be from Bend on the 20/126 through Sisters and along the McKenzie River to the I-5 and then north to Portland. It is highly unlikely the Old McKenzie Hwy (242) will be open before July (but you can keep checking).
Is there a reason you have to go as far north as Portland?