I don't think it's Harry. Or maybe it's just wishful thinking on my part ebcause it would undo some of the most potent Spider-Man comics I've ever read.

First of all, Harry and Peter made peace with each other before Harry's death - a great scene.

Second, Harry hated Peter for supposedly killing his father. If Norman Osborn was alive, Harry would have no reason to hate Peter. He might go after Spider-Man to make Daddy proud, but I think he'd rather try and break Norman out, rather than go after Peter and Aunt May. It might take some of the panache out of Norman, having Harry still be alive.

"Well when I talk to people I don't have to worry about spelling." - wannabuyamonkey "If Schumacher’s last effort was the final nail in the coffin then Year One would’ve been the crazy guy who stormed the graveyard, dug up the coffin and put a bullet through the franchise’s corpse just to make sure." -- From a review of Darren Aronofsky & Frank Miller's "Batman: Year One" script