Characters that I can confirm that are in:
Hunter (from Monster Hunter)
Rathalos (though I will admit that this one is shaky because they might've nixed it to only be in the Hunter's moveset for a Hyper because Giants might be done away with as playable, and Rathalos was planned to be part of the Hyper regardless)
Strider Hiryu
Leon Kennedy
Jedah
Nathan Spencer
Captain Commando
Spider-Man
Doctor Octopus
Venom
Songbird
Ms. Marvel
Ant-Man
Rocket (but Groot is now part of his moveset)
Black Panther
Doctor Strange
X-Men characters will be in, but might actually not be DLC.
Before you freak out, there's an asterisk by this, and that "only if the game gets delayed from its 2017 release date". Otherwise, they're DLC.
Don't get your hopes up too much, but don't lose it either.
Doctor Doom, Silver Surfer, and Super-Skrull are also in, but will be DLC as far as I've heard.
On the Capcom side of things, Captain Commando might be DLC and not a launch character.
The thing with him is that he might be moved to being DLC but is undecided as far as I heard.
GnG is seemingly getting a rep from what I know too.
But I am not in the exact know as to who, or if they'll be a launch character or DLC. Sorry.
I just know it's getting one.
As for the character itself, I don't see how it'd be anyone other than Arthur or Firebrand.
But I do suppose there is always the chance of them using Astaroth.
Regardless, be prepared for GnG getting a rep.
And don't bug me and ask me to know the rest of the roster. I only know what I know.
Hopefully this will tide you over.