Master Chief - Me, I think I know and understand Chief so much. I also have his voice.
OR (for a proper actor)
Jeffrey Dean Morgan, how about?
Cortana - Evangeline Lily OR Mackenzie Mason as the actual model and Jen Taylor doing the voice. She’d have to be CGI obviously.
Arbiter - Keith David doing the voice but the Arbiter will be CGI.
Sergeant Johnson - Keith David.
OR Idris Elba. Keith David would be awesome but he’ll also do the voice of the Arbiter, also he’s old as well but he’s probably perfect for Johnson.
Captain Keyes - Ed Harris.
Sergeant Buck - Nathan Fillion.
Miranda Keyes - Michelle Monaghan. Another Pic.
That’s all I got.