The Galactic Empire vs. The Galactic Alliance
The Empire under Palpatine as of RotJ
vs.
The Galactic Alliance as of the beginning of Legacy of the Force, with its internal strife issues handwaved away
+
The PT Jedi Order
The Empire has the advantage in numbers and superweapons, while the allies have the tech edge and a larger group of Force users.
I'd say they can win via a concerted assassination effort on Palpatine.