When are you headed up and back?

Donner is a no go if you are avoiding snow and Idaho as a whole would be best avoided.

Being you are from SoCal (no offense meant at all in this) you should carry chains with you regardless when in the mountain country and also carry some kind of blankets, extra jackets, flares (for starting fires and signalling) and emergency rations just in case the worst happens. Being you are probably both uncomfortable and unfamiliar with snow driving you would be better off being a little overprepared than thinking you will be able to plan a snow free route.

Let me know if you need a more specific list of what you should carry on a trip like that for safety.

Best route honestly is straight up I-5 then straight across to Idaho either at Portland or further up in Washington as most these routes are fairly snow free or at least plowed for heavy traffic.