looking for advice on fun roads that are accessible late May.

hi there, I am planning a 15+ day ride starting may 19th from Canada and touring into the US. crossing at the Roosville boarder (British Columbia to Montana) was wondering if anyone had some map route suggestions on Some warm weather twisties heading south. leaning towards using a western route and possibly making it to southern California but and very open to other suggestions for nice long reasonably warm ride. I ride a Yamaha fj-09 and like to keep it on the pavement if I can. thanx