Sorry if you do mean something totally different and I have totally misunderstood this project? Is it about building up the World United States Government?
First, we have to split up some states. Or do you really want to leave China with 2 senators and approx. 1900 electoral votes?
China should be split up into the 33(?) provinces. One can also make a case for splitting Guangdong, Guangxi, Henan, et al. into more states, as Guangdong alone would have approx. 160 EV!
As should India. One should make a case, a very good one, for splitting Uttar Pradesh (it has
nearly six times as many people as California, and thus ca. 300 EV!), Maharashtra, Tamil Nadu, et al. into several states, too...
Brazil can just be split into the provinces (although one State would have about 40 million inhabitants)
To Indonesia, the same applies: Provinces are your friend.
For Russia splitting proposals, I recommend
this map game. Of course, there, the countries are independent and many a time, they are red, but those are good divisions for Russia, although some are debatable.
How you split up Pakistan, Bangladesh and Nigeria is up to the local experts, but they must be split up anyway!
Even several European states should be split up according to the California Rule:
Germany:
I would propose South Germany (Baden-Württemberg+Bavaria+Hessen+ Rheinland-Pfalz) and North Germany, and North Rhine Westphalia. Even the 16
Länder on their own would be viable states (the smallest one, Bremen, would have more people than Wyoming!)
Turkey must be split into Thrace (with Istanbul), West Turkey, East Turkey, and Kurdistan.
Spain: Catalonia, the Basque state, and Galicia can be split off. Madeira and the Canaries can also go separate if you want more senators and more states to fiddle with...
Italy: Possible states are: Lombardy, Venice (=Trentino+Veneto+Friuli), Piedmont-Liguria (=Piedmont+Aosta+Liguria), Greater Tuscany (=Umbria+Marks+Emiglia-Romana+Tuscany), Lazio (=Lazio+Abbruzzes+Molise), Sicily, Sardinia, and Mezzogiorno (=the rest of South Italy).
Conservative would be Padania, South Italy, Sicily and Sardinia.
Other countries of Europe:
Then I would propose England+Scotland+Northern Ireland. Plus Wales if you want. Of course, Greater London or South England could still be split off...
Also, North and South France (like the Reverse Cold War), or N+S France plus Ile-de-France (a state with as many people as Florida!)...
Poland can be
just about left whole if you accept a state a bit over the California Boundary.
Austria (gets South Tyrol added!), Czechia, Hungary, Romania, Slovakia, Slovenia, Croatia, Bosnia, Serbia, Albania, Kosovo, Macedonia, Greece,... can be left alone as they are average US states.
The same applies to the Nordic and Baltic states. However, Finland should get Karelia added, and the Kola Peninsula.