Aaron Pierre, the star of the upcoming series Lanterns, will reprise his role of John Stewart in Man of Tomorrow. Pierre plays John Stewart, a member of the Green Lantern Corps, in Lanterns, so his involvement in Man of Tomorrow is somewhat obvious, as we've known from the get-go that Man of Tomorrow will pit Superman and Lex Luthor against Brainiac, an alien villain.
While we didn't get Hal Jordan or John Stewart as the DCU's first Green Lantern, Nathan Fillion makes a great first impression for the Green Lantern Corps as the snarky, egomaniacal Guy Gardner. For most of Superman, Guy is an antagonistic, reluctant ally, but his prickly attitude is best personified by how he fights in one of the film's climactic battles. When the Justice Gang flies in to help protect the people of Jarhanpur, he puts his ring to work taking out an army of Boravian soldiers and tanks. This includes making giant projections of human hands putting up their middle fingers, which knock the army's artillery around like flies being swatted. The whole fight sequence is pretty cathartic, but Guy giving fascist invaders the middle finger was one of the best summations of his character and the audience's feelings by the end.