Through the Gamerant site, later also published on NeoGaf, we have new information on the roaster of Marvel vs Capcom Infinite. It is also reported by a Reddit user that the number of characters will be expanded in the months following the launch, as has already happened with Street Fighter V. User Rikurikumore himself announced that the first DLCs should be Fantastic Four vs Dark Stalkers and X-men vs Street Fighter.
You can see below the list of characters present in the title.
Mega Man X
Hunter (from Monster Hunter)
The Marvel movies
Rocket (Groot will be part of the moveset)
All this information is however to be taken with a grain of salt, as it has not yet been confirmed by Capcom. But there may be more confirmations during E3.
Keep following Holygamerz for more information on Marvel vs Capcom Infinite.