Firstly, I would put this in the Me3 megathread but it is not actually about the third game
These are my thoughts on who and what,
Mass Effect: Contact
Director: Either Neil Blomkamp (District 9 and soon to be Elysium) or Christopher Nolan (Dark Knight, Memento, The Prestige, Inception) I would prefer Nolan because I think he could take a unique view on the IP.
Main Actors:
Shepard
Sam Worthington (Avatar)
or Russel Crowe
or Gerard Butler
Ashley
The only acceptable option:
The idea: The film would jump back and forth between two narratives. The story of Shepard's beginnings and the story of humans discovery of the Mass Relays and Alien species.