It s all highway. The most direct route is take I-15 to Pocatello which is straight north, then take I-84 to Twin Falls, then take Highway 21 to Sun Valley. They are pretty good about keeping the roads cleared off. If you wanted to go on to Stanley, that would be a problem because Galena Summit is usually closed in winter. Getting to Sun Valley shouldn t be a problem, though.
It s all highway ,Route it through Twin Falls ID and keep an eye on the weather Safe trip