To the Halo universe defence it would come to The Forerunners, the Precursors, the Covenant and the Flood. The UNSC even with Spartans included wouldn't be able to do much against the Star Wars universe armies. Specially since the Covenant demolished the UNSC with nearly no problem at all, The Spartans II just managed to slow it down. Who would win? Is hard to tell since the Star Wars universe is very advanced and if the Jedi and Sith would fight together against the Halo universe, then It's really hard to tell.