To start, No Guiseppe Garibaldi revolt. The Kingdom of Naples is humbled by the Papal States, the French Italian State and France itself, and Austria never ends up at war with Italy in the First and Second wars of unification. With a unified Italy, Napoleon now has a stronghold to use in Southern Europe and can mercilessly beat Austria into reputed destruction, and maybe, just maybe, no loss at Waterloo. Italy could have sealed the war for Napoleon.
Well, the first points are determined by what happens after the war, but really I'm not sure if the latter section is really all that certain, after all Napoleon had all the resources of Italy at his command up until the catostrophic loss at Liepzig caused Murat to strike a deal with Austria to keep his throne anyway. Why is having them as one state any different?
Anyway, lets assume that the scenario is that Murat does something stupid early on/dies and so Napoleon decides to unite the Kingdom of Italy with the Kingdom of Naples (which would be a bit odd considering that he would have been more likely to keep them seperate, but I'm willing to believe he could have been persauded to do it somehow). This still doesn't net Italy Latium, Tuscany, Piedmont or Liguria which were all annexed to France directly, but it's a pretty strong situation, and perhaps Latium is thrown in as a bit of generosity.
Problem is, I can't really see how this would change enough to let Napoleon win (as I said, the whole premise basically requires Murat to be out the picture for a start), and Eugene de Beauharnais, promised the title of King of Italy in the event of Napoleon having no further children, is unlikely to try and strike a deal to keep the throne as Murat did. Most likely, it's dismantled pretty much as OTL, but the Italian unification movement gets more of an early boost given the larger expanse of the Kingdom.