Resident Evil: Revelations producer Masachika Kawata has revealed that players will have to beat the campaign mode in order to gain access to the online multiplayer one.
According to Kawata, the campaign should take over 10 hours to complete. After which Raid Mode will be unlocked giving you access to online co-op and characters like O'Brian and Jessica. Kawata also mentioned that while this title is a portable one, the developers are aiming to bring the game up to the standards of Resident Evil's numbered games.
The 3DS exclusive will be available in stores starting February 7th 2012 in North America. Perhaps this is the game that the Nintendo 3DS needs to succeed.
Source: Sinobi Retailer Blog