I haven't been following much spoilers lately. Have there already been leaks on who's going to be on each show?
When it first came out, the idea was that Reigns/Rollins would lead Raw and Cena/Styles would lead Smackdown. With Cena being a part-time performer and Ambrose being their biggest full-time house show draw on the roster and already leading his own tours, Ambrose is likely going to be on the Smackdown brand to carry the house shows with Cena being part-time.
One live event card has been announced for post-Summerslam, and while it doesn't indicate any brand, the advertised matches are Ambrose/Wyatt, Orton/Styles and Miz/Cesaro which would point to it being a Smackdown brand live event with Styles and Ambrose being on the card.