The following information has been released by Cosmic Book News who have a history of exclusives that are either wildly inaccurate or on the odd occasion completely correct.
I would tend to keep the following spoilers in mind knowing that it is most likely incorrect:
• Most of the film is set in space.
• At the start of the film, Hal Jordan and Sinestro are paired to stop an intergalactic serial killer, Arkillo, who Sinestro later frees to join his Corps and restore order to the universe.
• Sinestro’s decision to leave the Corps is mainly due to his distrust of the Guardians and the fact he feels that the universe laughs at the Green Lanterns. Sinestro feels that a new Corps should replace them.
• Sinestro visits Warworld to recruit members to his new Corps.
• Sinestro frees Amon Sur and recruits him to his new Corps.
• There is a reference to Amon Sur’s previous attempt to destroy the Corps, which happened in Green Lantern: Rise of the Manhunters.
• Carol Ferris is kidnapped by Sinestro to draw Hal Jordan to him.
• Jordan requests that the Guardians deploy the entire Corps to Korugar to rescue Carol and defeat Sinestro’s Corps, but they deny his request. He subsequently makes a plea to the Corps via transmission of his ring. Several hundred respond and encounter Sinestro’s fledging Corps in a battle above Korugar.
• Hal, Kilowog and Tomar-Re use the large battle taking place above Korugar as a distraction to sneak to the surface of the planet to rescue Carol. There, they are confronted by Sinestro, Arkillo and Amon Sur. Hal and Sinestro evenly match each other, while Kilowog defeats Arkillo, and Tomar-Re defeats Amon Sur before they rescue Carol.
• The battle between the two Corps ends with the Sinestro Corps retreating due to the majority having little experience with the ring.
• There is a foreshadowing to the third film with a discussion by the Guardians mentioning that a “War of Light” is coming.
• Ryan Reynolds, Mark Strong, Blake Lively, Geoffrey Rush are all contracted to return for the sequel.
• Kevin Michael Richardson is expected to replace Michael Clarke Duncan as the voice of Kilowog. Update: Richardson previously voiced Kilowog in Green Lantern: The Animated Series and Green Lantern: Rise of the Manhunters video game and is the best guess to replace Michael Clarke Duncan, “sounds very likely.”
I have a feeling that we will not see a second Green Lantern film until JUSTICE LEAGUE OF AMERICA has been released and I’m not entirely certain if WARNER BROS would recast or attempt a reboot before tackling the above.