I really don't think this is the Julia and J.J. First of all, Julia kidnapped J.J., passed him off as Jack's son and he was eventually returned to his real parents. Secondly, he would be 3 at most now. I know soaps often accelerate the ages of the kids on the show, but the kid they showed today was at least 7 or 8, I can't imagine they would expect us to swallow that one!
Plus, Julia doesn't seem to have a clue who Jack is and seems very uncomfortable pretending that she does (as Jack's doctor wants her to).
I don't know, I guess anything can happen in the soap opera world, but I think this is just a coincidence. But, I think Jack will remember the good things about the actual Julia and they will end up getting together. Then, Carly will find him after he and this Julia are already together. That's just my opinion though, I could be totally off.