Back when I rode from Beaverton to Portland regularly I used to take Beaverton-Hillsdale up to multnomah village, then from there you can bomb down Capital Highway to Barbur then you basically have access to all of Portland from there, crossing Tillikum if you want to get to the East side. It's not the *shortest* route, but I considered it to be the least dangerous due to broad shoulders/bike lanes on Beaverton-Hillsdale.