Austria is the natural candidate, if Napoleon gave Austria the same treatment he gave to Prussia, then maybe Bohemia and Hungary can be separated, leaving Austria proper to the Hapsburgs, and these two new kingdoms to whoever he chooses.
Silesia can be detached from Prussia, and if he goes radical, he can banish the Hohenzollerns to Konigsberg permanently and give Brandenburg to someone else.
A part of Portugal was supposed to go to Godoy, this “Kingdom of the Algarves” doesn’t look very viable, Portugal is small and poor as it is, I can’t imagine any French Marshall consider having a piece of that to be a great prize.
Spain can be partitioned to at least Castille & Leon, Aragon and perhaps Navarre, however Joseph wouldn’t want to receive a mutilated kingdom, so either he stays in Naples and he gives Murat a piece of Spain or finds someone else for Castille and Aragon.
Assuming he gets to conquer Great Britain (unlikely), then Scotland can be detached from the UK.
If he campaigns against the Ottoman Empire and manages to kick them out of the Balkans, then Serbia, Greece, Romania and Bulgaria would be available.
Lastly, I am not sure about how to partition Russia, I’d think Poland would grow at their expense, but not sure if a Baltic or Ukrainian state is on the cards at this time.
I think Austria being partioned would be the most likely, you can get at least 2 decent size regional powers. If Napoleon didn’t do that in OTL is because I think he thought, he could ally with Austria or at least keep a balance of power to counter Russia and Prussia. He even married a daughter of the Austrian Emperor, not that it mattered in the long term. In hindsight, he should have dissolved the multi-ethnic Austrian Empire when he had the chance, they would have backstabbed him anyway.