At last word, the plan was for WWE Champion CM Punk vs. John Cena vs. Big Show to close Sunday's SummerSlam pay-per-view. There has been discussion of putting the title on Cena and doing Cena vs. The Rock at the Royal Rumble followed by Punk vs. Rock at WrestleMania 29. However, it's speculated that WWE will end up going with Cena vs. Rock II at WrestleMania.
speculation but this probably sounds more realistic than Cena vs Rock at Rumble & Rock vs Punk at Mania.