How can you know what a character is capable of before the game is on is even lauched? Everything will be pure speculation and we don't know the extents of his powers. AFAIK he might have his ass kicked in the end of the game in a embarassing defeat by Mercer and he becomes the protagonist again.
@NeonNemesis: Then that would be the setting for Prototype 3.I don't think you understood it, he might be hyped into growing more powerfull than Mercer, and then Mercer kills him in a embarassing way showing he's not even close to being a match for him.
You can't judge him only by trailers, you need story and the cutscenes to judge that, not to mention that there is also the possibility of many stuff being cut from the game.
I'll bring Legacy of Kain Soul reaver as an example where in the original version Raziel was suposed to drain a part of Kain's soul that would make him traverse between realms at will without the need of portals, he would adquire enhanced TK, possession, two more powerfull reavers amongst the other elemental reavers that didn't into that game, and killed Kain. Yet that game ended up in the hyperbolic chamber without none of those events happening since all of that was cut.
The same can happen here.
Well, by the end I assume James will be as powerful as Alex was at the end of the first game + the new tendrils power and the Blacklight Virus injection explosion. Anyway, Cole in Infamous 2, at the ending has an incredible array of powers, considering they are both ice and fire, + electric rockets, blasts and the ionic powers, not to mention that if he is the bad ending Cole, he gets The Beast's power. Basically, it goes like this: Good ending Cole is beaten by Heller, bad ending Cole stomps Heller.
We actually don't know about Hellers power-level yet, but I don't expect him to be weaker / much weaker then Mercer, so I would say Heller.
Mercers regeneration at the end of the game was impressive. His devastating attacks were powerful and his ability to to consume other people and morph into them would be great for sneaky attacks.
Mercer > Heller > Cole
But maybe that's just the fanboy in me talking.
Heller should take this from what I've seen. Cole has no way of getting away from Heller, who displays greater movement speed and reflexes than Cole has. Although Cole should be on level with his future counterpart Kessler, he hasnt shown movement or reaction speed anywhere close to Kessler's levels.
Heller will in fact be able to tank Cole's electricity powers, and should be able to tank most of his other abilities given his durability showings and healing factor.
But none of this really matters. Heller's massive versatility, strength, damage output and speed advantage makes for a very dead Cole McGrath.
Eventually Heller will be as strong as Mercer (if he's going to try and kill him anyway). Mercer could beat Cole and as Heller has all his abilities (plus a few more I believe) Heller should take this. We really need to play the game first though.
James and Alex would destroy Cole easily. Almost every attack they have will kill Cole instantly or very seriously hurt him.
The only way to kill Alex is to fully consume him (which James didn't do, he tore his arms off and threw them to the side, and didn't consume them, meaning Alex could come back and is still alive), he took a nuke and instantly came back. Cole would disintegrate. Their resistance to damage is also much higher than Cole's.
They both also have a HUGE intelligence advantage over Cole (they gain the knowledge of everybody they consume, which was a lot of people, including scientists), so that gives them a big advantage when it comes to gameplanning and what-not.
As for strength, that easily goes to Mercer and Heller. At the beginning of Prototype 2, Alex effortlessly picks up a tank with one arm and flings it like a frisbee. That gives them an advantage in punching and kicking power in close range combat (one hit will likely kill or seriously injure Cole, especially with Alex's muscle mass power-up), and they can also use projectiles.
The devastator attacks would put an end to Cole very quickly. Of course, they can shapeshift their body into weapons, and can pick up weapons from soldiers and use them.
Really, I don't see how Cole could beat either of them.