From Comic Book Resources:
Chicago-based rapper Common talked to Superhero Hype about going to guns in a comic book movie. "I just like to go out for good roles, anything, that's all it is really," Common said, "whether it's a comic book or true story or whatever it may be. I wanna be a part of great projects, but yeah, I'm familiar with Green Lantern because I collected (them) when I grew up." When we asked how the "Justice League" auditions went, it was obvious that he had been prepped well by his handler, because he said with a smile that he couldn't talk about it right now.
Which of the Green Lanterns he plays isn't made clear in the brief article, but my guess is John Stewart (second from right).