Update: October 15, 2014
JUSTICE LEAGUE Villains Revealed and GREEN LANTERN's Role
[SPOILERS AHEAD] It was recently reported that Brainiac will be the main foe in Justice League, and according to a new report over at Badass Digest, that is indeed the case. Who will take him down? Well, the initial team is made up of Superman, Batman, Wonder Woman, Cyborg, Aquaman and The Flash. Green Lantern is obviously missing from this roster, but he will apparently play a key role in Zack Snyder's Justice League: Part One as he arrives on Earth at the end of the movie - after Brainiac has been defeated - to warn the League that an even bigger threat is on the way; Darkseid!
The site confirms that each of the heroes mentioned above (minus Green Lantern) will show up in Batman v Superman: Dawn of Justice, "to face the larger threat that has manipulated Lex Luthor and maybe even Bruce Wayne."
All of this apparently comes as a result of Superman's Kryptonian beacon from Man of Steel, and that it does indeed lead Brainiac to Earth. The World Engine also destroys at least part of Atlantis, hence what brings Aquaman to the surface, while the site goes on to add that as previously reported, General Zod's corpse does play a big role in Batman v Superman.
JUSTICE LEAGUE Movie Villains Revealed; New Details On Green Lantern's Role