The thing is, without Dion as leader I'm guessing an election is held a lot earlier - Dion went down in the polls somewhat quickly and the Liberals weren't exactly eager to bring down the government until this reversed itself. Without Dion I'm guessing an election is probably held about a year earlier than OTL (when IOTL, it's worth noting, the Liberals were in a more competitive position).
McKenna has a pretty respectable reputation, so I think he'd do the best out of anyone, and in my opinion be likely to win a 2007 election.
Iggy, as OTL proved, would clearly be vulnerable to attacks, but despite the end result of the 2011 election he seemed to be running a pretty solid campaign before the "Orange Crush" occured. And while I'm not saying that couldn't happen again, I don't think it's very likely, as at that time the NDP had only just begun building itself up un Quebec. All in all though I think he does slightly better than Dion, but not by very much.
Rae, like Iggy, would also be vulnerable to attacks, but of all possible leaders (even, I think, McKenna) he's the best politician of the bunch. The man knows how to run a campaign and how to harass the government in the House of Commons. I think he'd probably do better than Iggy would in this scenario (and definitely better than Dion IOTL), but more than anything else he'd likely cause NDP voters (who, as I remember polls showing, generally tended to like Rae) to shift their support to the Liberals.