James Gunn is known to be a very efficient director, and Superman: Legacy seems to be a great example of that. It's only been two weeks since we learned who the new Clark Kent and Lois will be, but he's been very busy casting other parts of the movie as well.
Vanity Fair has the honour of announcing that Nathan Fillion will be Guy Gardner's Green Lantern, while Isabela Merced has been cast as Hawkgirl and Edi Gathegi is set to play Mister Terrific in Superman: Legacy.
This does, unsurprisingly, mean Fillion won't return as T.D.K in the new DCU after making a short appearance in Gunn's The Suicide Squad, It also adds another actor to the "Moving from Marvel to DC" list, because Edi Gathegi played Darwin in X-Men: First Class in 2011.