No way, he'd definitely play wing back imo. Not sure why people think Di Maria wouldn't be able to play the role. The most important thing for playing wing back in this system isn't actual defending, but stamina. In this respect Di Maria is definitely among the best in the world. He may not specialise in tackling, but I'm sure he'd be able to do the job, especially with Van Gaal coaching him in training. Cuadrado's not any better defensively imo, but people don't have any problem with him playing there.
De Gea
Jones, Smalling, Evans
Young, Carrick, Herrera, Di Maria
Mata
Van Persie, Rooney
Judging by pre-season, there is absolutely no way that either Wayne or Mata won't be first choice and one would assume Van Persie will be a starter also. Van Gaal also clearly rates Welbeck very highly so signing another player to play in the front 3 positions wouldn't make sense. Welkeck, Januzaj, Kagawa and Wilson will likely all have to be content with a place on the bench as it is.