Only if we got balkanized, and the best chance was in the first years of independence and the turbulent years of the Regency for Pedro II.
It's actually pretty remarkable that Pedro I managed to hold the country together, and laid the groundwork for our survival as a unified nation. Even with all his failures (both personal and moral), he have a positive legacy in the end.
Latest date possible would be in late 1830's. Even if Farroupilha, the Cabanagem and the Balaiada still continue after Pedro II ascension (he took power at the age of 14, after a popular movement), the country was becoming more stable and united.
If Brazil was to be the smallest country, it would probably include Rio de Janeiro + Espirito Santo, and even so, it would require Uruguay to be bigger, or not existing at all, and i'm not speaking of the Guianas..
Maybe you can do it with the "Inconfidência Mineira" (A pro-republican conspiracy in the gold-mining regions of Minas Gerais) being more successful, with Joaquim Silverio dos Reis failing to deliver the conspirators to colonial administration. With such a POD, maybe the revolts in Bahia could be more sucessful, and similar movements could arise in Ceara and Pernambuco in the Northeast, and in Grão-Pará. Not sure if regional spirit was already high in late XVIII century in the Brazilian South.
Brazil was not very stable and it wasn't that populous in the times that Uruguay was our province, even if we got a advantage in numbers to Argentina already. Brazil only truly developed only after the Paraguayan War.
The spanish couldn't truly enforce Tordesilhas in Brazilian territory, by the times they tried for real, it would have been fait accompli.