I took the photos I found on Google and changed their appearance and you need to copy the URL because it won't upload on the page (I can't get the hang of that)
First off the main character of course:
Ewan McGregor as John "Soap" MacTavish
I think McGregor would good as he a thick accent like Soap and that the mohawk would work. Although, he wold need to bulk up a bit, tan, and get brown hair but he could do it.
Willem Dafoe as John Price
Dafoe is pretty good as he kinda looks the part as long as he has a beard (and of always have a hat). He'll need a british accent but you know he can do one cause it's Willem Dafoe
Gearad Butler as Gaz
Okay, this one is one to think about. Butler looks only a little like Gaz with a beard and the hat, but, he's good enough to pull off being gaz with the accent.
Terrence Howard as Paul Jackson
I think Howard would be pretty good on this chracter as he might look like him (we don't exactly know Jackson he looks like) and that he's a good at protraying soldiers
Sacha Baron Cohen as Nikolai
This one is little odd (an I found other people who might fit him) but Cohen was able to do all those other characters from different countries and I bet he could do Russian. Plus, Nikolai might be used for some comic releif. Hr'd be helpful, annoying, snd we miht "love to hate" him.
I had a picture of Mark Strong for the antagonist Zakeav but it won't upload for some reason (also he might work better as Zakeav's son but Strong has had his fair share of being the bad guy)
Those are my ideas for the Modern Warfare film
If anyone has other ideas (epspecially for Zakeav) go ahead and contribute.