There are a couple of big differences between Tito's Barcelona and Guardiola's. Tito seems to like a faster tempo, and he is always counting a lot on his wingers (Tello, Pedro and Alexis) to create some space down the field and open up the defensive line of Barcelona's rivals.
They are also having some trouble defending counterattacks. Their defensive transition is not good whatsoever since Alex Song hasn't been playing as well as expected in the centerback position. As a matter of fact, they've been playing with two defensive midfielders in the defensive line: Javier Mascherano and Song. Gerard Piqué is still recovering from an injury, but even though reports say he's doubtful, the Spanish defender will likely be on the pitch alongside Mascherano, moving Song to the bench.
Barcelona's new leftback Jordi Alba isn't having a very important role so far. It's true that he's had a very long season playing both the UEFA Eurocup and the Olympic Games, but Tito might also be a little concerned about having two very offensive fullbacks on the pitch at the same time considering how many counterattacks his team has been conceding lately. Adriano was sent off in Bernabéu's Supercup match against Madrid because Cristiano Ronaldo was probably too much for him, so Vilanova will have to make a risky decision for the leftback spot.
Barcelona's coach has been rotating his players a lot. Iniesta, Xavi and Messi have not been on the pitch together for many minutes this season even though the three are healthy. They will surely feature against Real Madrid.
The defensive midfielder spot is property of Sergio Busquets. He knows what he has to do in Barcelona's 4-3-3 formation, so it's very unlikely that Song starts this game in his position.
Tito's real decision will come when he has to choose his wingers. Villa, Alexis, Pedro and Tello are all healthy and competing for just two spots. If Vilanova doesn't want to surprise Mourinho, he will start Pedro and Alexis. That's what everybody's expecting. But Tello is a quick winger that could cause Arbeloa some trouble in Barcelona's left wing. The Spanish defender will be much comfortable defending Villa. He's not physically at his best and is a much slower player than Pedro, Alexis or Tello.
One way or another, this version of Vilanova's FC Barcelona seems vulnerable. If Madrid is able to play a decent game, Mourinho's team should be capable of creating a couple of really good scoring chances. Then, the game will depend on their accuracy.