The two-player multiplayer campaign mode will see each player taking turns to move their armies across the map, with a set time limit agreed upon by the players limiting the length of each turn, according to an interview with CA's Mark Sutherns on PCFormat. nope "Players will certainly have the option to take control of the AI armies in battle against their opponent," added Sutherns. "Another option we're looking at is to allow a spectator mode on battles."
The fog of war will act as it does, though Sutherns noted that players cooperating against the AI may have an option to drop the fog.
Sutherns also explained that the game's diplomacy systems will need to be changed for the multiplayer campaign, and will become a focus for the team following tomorrow's release of the full game.