In a welcome twist, the game also supports online play through friendly and ranked matches. (gamingunion.net)
The reason I think this to be true is because all the quests are available for the 3DS version, and the 3DS version doesn't support online play. (teamworkcast.com)
Watch Dogs will also support online play with modes similar to Dark Souls and others similar to GTA 5. (nonfictiongaming.com)