The chance of them getting any actor who isn't already really well-known for a movie like this is probably close to nil. They've got the fact that it's the Halo franchise, now they just want to make it sell even more, so they'll stick some ******* in a suit into the movie (All of the sudden, Gerard Butler popped into my head - please god, no) and tell everyone who it is so they can be like "oh, but *insert name* is in it so it has to be good!"
As it is, to the guy who said it should be a cross between District 9 and GI Joe:
District 9, yes. Definitely. Blomkamp worked on that stuff, and you saw his Halo work or else you get banned from this site for being a heathen.

(just kidding)
GI Joe? Idk if you've read Stig's rant (If you object to offensive words and massive hate, don't.), but he has it spot-on. I don't know why anyone ever followed a Beattie script for anything, the man is a retard. In GI Joe, he focused too much on putting in movie cliches, comedy, he even thought that ice sinks.
That, and the Delta-6 suit motions looked terrible. And those are obvious MJOLNIR knock-offs.
I'd much rather it be, say, a mix of SPR (for the quality acting), District 9 (because it's been proven that Blomkamp and WETA can do great and wondrous things), and if we can boot Beattie's script out and use, say, Alex Garland's original again, then we might have something there.
EDIT: Actually, now that I think about it, you could use the goddamn book itself as a script and it'd be better. I've always wondered why nobody does that. You can take artistic liberties with how battles play out, add in scenes and stuff, but seriously, for movies like this where the script is based off a book... your script was written long ago.