2. Donald Glover (as John Stewart)
Glover made his bones very early as a staff writer for "30 Rock" while he was still living on campus at NYU. Since then he's become huge for his role on "Community," his small part in this last year's The Martian, and his rap career under the name Childish Gambino. He's a funny guy, but he's also capable of great gravitas. I submit that his John Stewart would be a fantastic foil to the reserved do-gooder of Hamm's Hal Jordan. It's another fantastic buddy-cop pairing... only this time it's in SPACE!
The Green Lantern lore requires an audience surrogate character. Jordan and the other members of the Corps can explain everything to the audience by explaining it to rookie Stewart, and Glover's wide-eyed innocence and enthusiasm would be just the palate-cleanser after Ryan Reynolds played the rookie in this universe by essentially saying, "It's cool. I'm so awesome that I instantly understand everything... anyways, I quit."