A post on the Bioshock 2 forums seems to confirm that Bioshock: Sea of Dreams will be "mostly a prequel" to the first game.
The post also shows a picture of one of "New Daddy's" "experimental suits" (pictured above).
Full entry below:
Seeming that Bioshock 2 is going to be mostly a prequel. One of the greatest things too look forward to is what to expect of the Big Daddy. In the picture you can see a sneak peak of one of the big daddy's experimental suits. One of the new weapons that the Big daddy's will have is an archaic looking wooden cannon. The tank on his back is a lot smaller than what we're use to seeing, and the gloves and pants are more of a leather rather than the traditional Diver suits. And probably the most noticeable change that the "New Daddy" has is the helmet, it only has three sight holes, and they are all forward facing. Whereas the Big Daddy's helmet has multiple sight holes and they give multiple angles of sight.
Update: It has been brought to our attention that this information might not be as reliable as first thought. Therefore, it's filed firmly under "rumour" for now.
By Mike Bowden