Napoleon Bonaparte was born in 1769, the same year that Corsica joined France. If you have a POD before his birth it will most likely butterfly him away. But, if we assume that he is still born as the Napoleon we know and despite differing social conditions matures into a similiar person as the historical figure, then this can be workable.
Before being subjugated by France in 1769, Corsica was an independent republic, founded in 1755. That's fourteen years for the island to be aquired by someone else. Before independence, Corsica was a Genoese possesion. Giving the island back to Genoa wouldn't be a good idea because Genoa at this time had been almost completely subjugated by France. And of course we want Napoleon out of France.
If Napoleon is going to be a military mastermind he needs to be trained in a military academy. In OTL, he underwent his training to become an artillery officer at the Ecole Militaire in Paris. The only military academy in Italy is the Accademia Militare di Modena, located in Turin of the Kingdom of Sardinia. Before 1798 the academy had neither a military engineering school nor an artillery school, so Napoleon will have to find another early specialty.
Now, we need to have Corsica stay independent after Napoleon is born and have him wind up in Turin, training to be an officer. Keeping Corsica independent is hard enough. Genoa still had a claim to the island, but they had long since given up hope of controlling the island. They also had large debts, which in OTL they paid off by selling that claim to the Kingdom of France. The easiest thing to do would have been to have Genoa sell their claim to the Kingdom of Sardinia. Unfortunately, King Charles Emmanuel III of Sardinia might not have had the money to aquire the rights nor the desire to subjugate the island. That is the kind of question we need an expert for. Also of note is whether France, which dominated Genoa, would interfere in the proceedings. If, somehow, France keeps their nose out of it and King Emmanuel III has the money and the desire to buy the claim then you have just made it a lot easier for Napoleon to get from Corsica to the military academy in Turin.
According to Wikipedia, in 1767 the Corsicans took the island of Capraia from Genoa, which caused Genoa to ask the French for help, ultimately ending the Treaty of Versaille, in which Genoa sold their claim over Corsica to France. If you keep Corsica from doing this then the island nation might be able to hang onto her independence a little longer, though eventually Genoa will ask France for help, which is why I typed out the above scenario. As a side note, the above would have to happen before 1767 but not too much before because we don't want to butterfly away Napoleon.
So, if you go with scenario one, we'll say in 1767, Genoa sells its claim over Corsica to Sardinia. Then, King Emmanuel III invades and conquers the island. Two years later Napoleon is born. Actually, Napoleone di Buonaparte is born; ITTL he won't change his name to make it sound more French. Because Napoleone's parents are somewhat affluent, he will most likely study abroad, probably in this timeline somewhere in Piedmont. At the age of 15 he can enroll in the Accademia Militaire di Modena. We still have to pick an alternate field of study for him. After that we have his rise to the top.
The Napoleon we known was greatly benefited by the French Revolution, which allowed him to make a meteoric rise through the ranks of society to the very top. Here, we basically have two options. Create our own Sardinian Revolution or have Napoleone become a favorite of King Victor Amadeus III, giving him the backing of the Kingdom of Sardinia.
Either way, Napoleone is going to have a very hard time carving out his own Italian Empire. The Kingdom of Naples-Sicily and the Grand Duchy of Tuscany are both in personal union with the Austrian Empire. The Republic of Genoa isn't going to go without a war with France, though if the French Revolution occurs on schedule Genoa could be snatched. The Republic of Venice, which by this time is long past its golden age, is protected by a strip of Austrian land between it and Piedmont. Of course, attacking the Papal States would be suicidal, as all of the catholic kings would come to the rescue of the pope from the upstart Sardinians. The Bishopric of Trent is also under the authority of Austria. The Duchy of Parma is ruled by Don Philip, attacking it would incur the wrath of Spain. Only the Duchy of Modena and Reggio, i.e. Este, and the Republic of Lucca can be taken without foreign entanglement.
What you need is for the French Revolution to still occur and the War of the First Coalition to happen. In it, France could agree to let Sardinia absorb Genoa in exchange for Sardinia distracting Austria by attacking its italian possesions. This allows Napoleone to start building his Italian Empire.
Phew, that was a long post. Now I'm starting to feel like turning that into a timeline.