Well Which Ending did they say was Cannon?, what all this Means is something Different depending Upon Which side of the Coin it Landed
if its the Good Ending, maybe someone has rebuilt Rapture, or at some point, someone treid to Establish a Second one Based off the first cause 'there sure they can do it right this time'
if its the Evil Ending, who is to say jack was Content with the ADAM he stole from the First set of little sisters, and is now after he is Sure he got all of Them(i would say the Amount you Actually Saved was not all of them, there may have been More then that and there just not Anywhere near where you were, i mean the city itself looks rather large, and there's parts you cant get too) and as was stated Earlier someones gone looking for there daughter, or Perhaps this time your Tennenbaum going back to stop jack from harming any more people
and as for which one this is for, since its confirmed there's a Movie AND a Sequel, it can be for either