"Welcome to Geekenstein’s first edition of “Casting Call” where we pick our favorite actors to portray characters from our favorite games and comics. This series is going to be a combination of creative writing and photoshopping. First up, a personal favorite of mine: Gears of War. Enjoy!" - Craig Kandiko of Geekenstein.com
Then if they would ever decide on full-CGI I would suggest something like those in the CGI-base Starship Troopers Invasion with a mix of Resident Evil Damnation type would be a good design basis.. and simply put all the Gears trademark.
I don't know who he would play but you can indeed get him as one of the soldiers -he's super big...
He would fit perfecting as a believable gears of war solider
Best thing to do would be to pick a very specific event from the universe instead of trying to cover a whole military story. Focus on a handful of layered characters, both good and evil, and make it a horror story with short bursts of crazy intense action.
There are a lot of people like Carmine who looked small in the first game that they could hide in helmets.
A good example is the Halo: forward unto dawn series. They focused on character building first and then just threw in a covenant invasion out of nowhere without trying to explain what they are. We felt the same intensity, confusion, and fear that the cadets felt. I can just imagine a Berserker scene like that.
You also have to remember that before Marcus was in players hands he was in jail for a while while the Locust were fighting so we might see a band of warriors not even related to Marcus at all.