In a plausible XI comprised of current players AND players from the 2011/2013 seasons, I'd say you're looking at a single shoe-in from the current team: Bruno.
VDS in goal (obviously - he was better than De Gea is now at the point when he retired, that's just a facht).
Three out of four back there are given: 2011 versions of Rio, Vida and Evra...forget about it. It's a different class to anything we have now. The one question mark is the RB position. Is AWB significantly better than...oh, Rafael* or Valencia (in his RB incarnation)?
Midfield: Central midfield, that is. If you could replace any combination of McTom/Fred/Matic/Pogba with...an over-the-hill (but still pretty sharp) Scholes and a still prime Carrick...what would you do?
Attack: Again, Rooney in 2011 was a player on a different level than anyone we have currently. That really isn't debatable. And ditto for Van Persie in 2013. They were - arguably - precisely what we lack at the moment, i.e. undoubtedly world class attackers in their prime (not in theory, not potentially - they were first rate on the highest level, period).
Wide forwards/wingers: Well, there's a debate to be had there - depending on what formation you go for.
But you could very plausibly field Rooney on the left. A 2011 Rooney on the left in a typical 4-2-3-1 would replace Rashford or Martial easily. A 2011 Nani would do the same - and he could also, plausibly, be a better alternative on the right than anything we can boast presently.
Let's do a Ole style 4-2-3-1 then:
VDS
Rafael-----Rio-----Vidic-----Evra
Carrick-----Scholes
Nani-----Bruno-----Rooney
Van Persie
Yeah? Question marks over Nani (but we don't have a single player on our books who would undoubtedly do better than Nani on his day on a regular basis) and Rafael (but the obvious alternative here is AWB - who comes with obvious flaws, he is better defensively but has been decidedly mediocre offensively so far).
In my opinion, that's ONE single player who would
undoubtedly walk into said set-up (Bruno).
* Fabio (who actually started for us in the 2011 CL final, lest we forget).