According to Extric from the official PlayStation boards (linked above) M.A.G. is confirmed as a FPS only PS3 title.
A scan of the article detailing this from Game Informer magazine is available below, and to quote:
Okay, I just got done reading the MAG article in the latest Game Informer and here is the information on the games camera view:
The biggest change SOCOM fans will notice in MAG is the gameplay perspective; Zipper abandoned the third-person perspective in favor of a first-person experience.
"We looked at the number of different camera options for the game, and settled on FPS primarily because of the scale of MAG," Bodewin remarks. "Some of our previous games were third-person, and it was well suited to [managing] teammates and AI quadrates as well.
But for a game of this size we really wanted to make it the most immersive and the most intense large-scale game that we could. There's really no better way to do that than to sink you right into the action and look at things through a first-person perspective."
Here is a picture of the paragraph where I got the information from. Best one I could get because the flash kept getting in the way...
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