Bikieboy's route is a good one, but if you want a slightly different alternative, a little flatter and safer, try the following:
Take Bikieboy's route to Causey Rd, but instead of turning right on Fuller, keep going straight - the road will curve around a hidden gem, a big-ass farm right in the middle of suburbia. If you follow the road around the corners, it will dump you out onto Monroe. Turn left, and ride Monroe up to the stop sign at Linwood. Turn right. Ride Linwood down the slope and turn left at the light (King Rd.) ride one block west on King and turn right on Wichita. Wichita is a low-traffic residential street - it'll take you roughly 1/4 mile to the Springwater Trail. Turn left there, and ride that until it dumps you off at Ochoco after 3 Bridges. Turn right and ride up to Umatilla, then left on Umatilla, keep going until you get to the railroad tracks and the start of the Springwater along the Willamette. Follow Bikieboy's route the rest of the way from there.