To specifically address your question - the coast ride is always nice and living in Portland you know the weather issues you may face in July on the northern and central Oregon coast. East from Portland would be vastly different but I also very much enjoy that ride, particulary through Oregon. I like the high desert side of the Cascades, and there is minimal traffic. Again, in July it will be warm. Whichever direction you take, you might wish to follow the ACA route for those thousand miles.
Let me add that the California coast, particularly from Fort Bragg south to the Central California coast, can be foggy and cool in that time of year. You know the saying from Mark Twain, the coldest winter I ever spent was the summer I spent in San Francisco. And Route 1 is narrow, very narrow, and twisting in Sonoma county.