Michigan to California this December

Definitely would only consider the southern route. I wouldn't even consider the northern route. Who knows what the start to winter weather will be this coming here? Pick up a few jugs of antifreeze if needed on the return trip. You sure don't want to get stuck on the interstate if they decide to shut it down and not be able to take precautions as much as you are able.
We got stuck in Tucumcari, NM one year in Dec for 13 hours on the highway. It's definitely doable. Just have to be prepared for the possibilities.