Australian-born Alex O'Loughlin may not be well-known to movie buffs, but Hawaii Five-0 fans know he's a leading man in the making. With the looks and swagger of a tropical cop, O'Loughlin more than looks the part of Hal Jordan (and was considered for the role of James Bond before Daniel Craig).
Playing naval officer-turned-detective Steve McGarrett, O'Loughlin is no stranger to action, given the show's 'new movie every week' structure and style (this is a Kurtzman and Orci joint, remember). Following a star like Ryan Reynolds is a challenge for any actor, but the real hero of Green Lantern was Jordan - a fighter pilot that exudes cockiness, insecurity, and a sense of humor; contradictions more easily said than done, but O'Loughlin pulls it off on a weekly basis.
Recasting Hal Jordan could be the riskiest move for WB, but entrusting the job to an actor who is somehow both proven and a relative unknown would definitely help hedge their bets.