If a Modern Warfare 2 movie is ever made, I think it should focus solely on Task Force 141 and avoid the "boring" Army Rangers/Ramirez segments of the game. Here are my picks for Task Force 141 and the major antagonists.
John "Soap" MacTavish: Ewan Mcgregor
Mcgregor is the spitting image of Soap and he can do the proper accent. Not to mention he's quite the good actor.
Captain John Price: Liam Neeson?
If you say I'm completely wrong on this one, you're probably right. I went through probably thirty possible actors for Price and none of them felt right.
Simon "Ghost" Riley: Tim Roth
Let's get one thing straight: Tim Roth is a badass. Ghost is a badass. They're both English. It's a perfect fit.
Gary "Roach" Sanderson: Karl Urban
Really, ANYONE can play Roach since we never see him or hear his voice. I picked Urban because I feel that an Urban-Roth-Mcgregor combo on screen would be awesome.
General Shepard: William Hurt
Just look at the pictures. Should be enough. Seriously though, he basically WAS Shepard in The Incredible Hulk.
Vladmir Makarov: Joseph Fiennes
After going back and forth between Fiennes and Gary Oldman for this role, I decided on Fiennes because, well, he's younger. Plus Oldman is already Viktor Reznov.