That's the million dollar question, and proves the ultimate tactical chess match for Manchester United manager Sir Alex Ferguson.
Who he chooses to play, and in what alignment and system, prove to be they key questions in the preparations for this Clash of the Titans.
Phil McNulty of the BBC analyses the challenges posed to Ferguson as he preps for Barca.
It was Ferguson who coined the term "carousel" to describe Barcelona's passing, movement and mastery in possession, and United's last ride resulted in head-spinning humiliation as they were outclassed in the 2009 final in Rome.
Barcelona coach Pep Guardiola's presence at Old Trafford on Wednesday was almost as academic as Schalke's as United completed a trouble-free passage into their third Champions League final in four years with a 4-1 win that sealed a 6-1 aggregate victory.
The question that hung over Old Trafford's celebrations was not could United beat Schalke - this was answered by an atmosphere devoid of tension and Ferguson's selection of his second string - but could they beat Barcelona?
Ferguson has bullishly insisted ever since that balmy night in Rome's Stadio Olimpico that he knows exactly what went wrong with a United side that walked out as favourites and walked back well beaten at the conclusion of a chilling exercise in ball chasing.
He now has the perfect stage, the very place where United won their first European Cup against Benfica in 1968, to put his theory to the test. And he can be assured Barcelona will present the most searching examination.
I asked Ferguson if his belief that he knew the precise points where United's game plan came apart in Rome increased his confidence that the outcome will be different when they confront Barcelona again on 28 May.
He said: "I don't think we should be going there lacking in confidence. We are playing a fantastic team but they shouldn't hold any terrors. We can't be frightened out of our skins because of that. Our job is to find a solution to playing against them."
Guardiola will have gleaned little from his spying mission to Old Trafford as there was nothing to spy on. Ferguson made nine changes from the team that won in Gelsenkirchen, with Wayne Rooney given the night off, and it was still more than good enough to beat a Schalke side who gave a very bad account of themselves in this semi-final.
Darron Gibson, despite recently leaving the Twittersphere, gave eloquent answers to the critics with a decisive early contribution to snuff out any lingering aspirations the Bundesliga team had of overturning a two-goal deficit.
He set up the first for Antonio Valencia and scored the second himself, aided by a dreadful error by Schalke's coveted keeper Manuel Neuer - who looked as bad at Old Trafford as he looked world class in Gelsenkirchen.
Jose Manuel Jurado's goal was a minor inconvenience and Anderson restored reality to the margin between the sides with two late goals.
So United's thoughts turn to Wembley, a happy destination for Barcelona also as they secured this trophy for the first time underneath the old twin towers with victory against Sampdoria in 1992.
And a player who may just figure prominently in Ferguson's thinking will have delighted his manager by making a 17-minute comeback as a substitute following an absence through illness.
Darren Fletcher is one tool Ferguson may use to try to dismantle the carousel, badly missed when suspended in Rome and a character his manager trusts on the big occasion - and do they come any bigger than meeting Barcelona in the Champions League final at Wembley?
Ferguson said: "Some players are big game players and Darren Fletcher is a big game player. A perfect example is Mark Hughes, who was one of the best big game players in Manchester United history. He never failed in a big game and that's the type of example we can see in Fletcher."
United's manager must decide whether to stick or twist at Wembley. Rooney and Javier Hernandez have formed a fruitful partnership, but dare he risk playing both against Barcelona and risk the prospect of being outnumbered in midfield?
United were run into the ground in Rome, a task always made more painful when it is done without the ball, and the general opinion is that Michael Carrick is only just completing his footballing rehabilitation from the trauma visited on him by the brilliance of Xavi and Andres Iniesta.
Ferguson's default option, the one that makes him a worthy member of the ranks of all-time great managers, is a natural instinct to attack but pragmatism will also play on his mind also as he formulates his plans.
He may, in his ideal scenario, wish to fight fire with fire and take Barcelona on. This is a strategy with high risks attached as few sides have ever been as well-equipped to take on such a task as one with Lionel Messi at its heart and master finisher David Villa added since their victory in Rome.