In English, Miller's voiced by... no, not Cam Clarke, but Robin Atkin Downes, aka Travis Touchdown and Medic. His delivery is pretty darn similar to Cam Clarke's Miller, though. There's also some Fridge Brilliance in not casting Cam Clarke: Cam Clarke never voiced Miller himself, but an imposter posing as Miller.
Chico is voiced by Kikuko Inoue, who voiced Jaime Seed in Snatcher, Karen Hojo in Policenauts, The Boss in Snake Eater and Rosemary in Sons of Liberty. And since cute boys are not her usual forte, this counts as playing against type.
Strangelove is voiced by the same voice actress and model of Raging Raven, Yumi Kikuchi, in Guns of Patriots. On a related note, Strangelove is also voiced by Vanessa Marshall, who voiced Olga Gurlukovich in Sons of Liberty (whom she bears a slight resemblance to), and EVA in Portable Ops.
Hot Coldman is voiced by the same voice actor as Sigma from the Mega Man X series and one Kinzo "DESIRE" Ushiromiya in the Japanese Version. In America, he is voiced by H. Richard Greene (AKA, Congressman Robert Royce from The West Wing)
Kojima originally had no intention to direct Peace Walker. He intended to write only a rough outline of the game's plot and leave the rest to his younger staff, much like he did with the previous PSP games in the series (the Acid series and Portable Ops), but he changed his mind when his younger staff did not understand the story's theme of nuclear deterrence.
A dinosaur version of Metal Gear RAY, named Gear RAY, was supposed to appear alongside Gear REX during the Hunting Quests.
The train that Snake was supposed to stop the shipment of nukes by the Peace Sentinels was originally intended to be a playable level. If the storyboards are of any indication, that train would have ended up being shot off the tracks and plummeting.
Peace Walker was originally supposed to heavily resemble Metal Gear REX, down to the railgun and even the design of its hangar was supposed to mirror REX's hangar on Shadow Moses.
Paz and Zadornov would have been discovered earlier to not be trustworthy (especially Paz), where Paz and Zadornov are overseeing its construction, and Big Boss discovers their affiliation to the Peace Sentinels by eavesdropping from a window in a manner very similar to how Solid Snake eavesdropped on Liquid Snake and Revolver Ocelot's conversation in Metal Gear Solid before Coldman finds and surrounds him. Coldman was intended to be killed by Zadornov alone with a gun to the head, and at some point later, Paz would actually do the very same to Zadornov before hijacking ZEKE. If some of the storyboard sketches were anything to go by, Big Boss was apparently going to actually lead his troops on a sneaking mission rather than going in alone. An entire character model, the AI lab workers, who were implied to be of German origin, was also cut.
Working Title: Was titled Metal Gear Solid 5 early in development.