yes, Call Of Duty 3 for the PS3 supports online play, up to 16 players in a game.
Out of curiosity, what do you have your PSN account set up for as the residence? One thing about Resistance is the servers for this game are regionalized- those set up for Japan can only play Japanese-area gamers, USA/ Canada gamers hook up with other USA/ Canada gamers, etc. This could be part of the reason why you can't seem to find anyone online in Resistance.