While a Reigns or Orton confrontation with Lesnar would certainly be fresh, the smart money is on another confrontation of sorts with John Cena. Cena and Lesnar could square off again at the Royal Rumble, although there are conflicting reports about whether or not that will no go ahead. In advertising for the event, Cena is listed as an entrant in the Rumble, something he couldn't exactly do if he was in a Championship match with Lesnar. On the other hand, on the most recent episode of Raw Paul Heyman said (in a fantastic promo) that if Cena gets past Rollins on at TLC that a battle-weary Cena would have to take on a fresh Lesnar. Could this be at the Royal Rumble? Cena/Lesnar III (or IV if you count Extreme Rules 2012) seems to be what WWE is going for. At the Slammys, Lesnar will no doubt send a message to Cena on the programme.
