You generally can use frontage roads along the I-5 corridor, or the ACA Pacific Crest route has much less climbing in Oregon and Washington than in the Sierra and Southern California, plus you can cut out more of the climbing by skipping Crater Lake. Here's a fellow that headed north along it in the late spring of 2012. crazyguyonabike.com: Bicycle Touring: Free Range Retiree-2012 Ride (S.Pacific Coast to the Sierra Cascade Route N), by Art Birkmeyer

They had some late spring weather fronts go by once he was in Oregon, which are generally followed by northerly winds, so he had one day of headwinds. Not something you'll encounter in the middle of summer, though. In my experience in around there and in the Sierra, you will encounter little if any wind in the morning, followed by upslope winds in the afternoons--that is, winds will blow up toward the crest of a range from either direction. An exception is in the long trough east of the Sierra with a strong 4-corners high pressure system providing a southeasterly monsoon flow--we encountered strong southerly winds in that situation.