with the POD set at death of Dom Joao VI (1826) and decided to retain both crowns:
ruling from Brazil: definitely loses Portugal. Probably loses Brazil, as they're ticked at him for blowing money and losing the cisplatine war (OTL), and now they're also ticked at him splitting his time with the portugese (which they were to a good degree OTL with his attempt to place his daughter on the throne, but which would get racheted up big time with a reunion attempt). Meanwhile, Portugal isn't going to accept being second fiddle to Brazil, so they simply dump him and annoint a new King, or go republic.
ruling from Portugal: Probably keeps Portugal. Getting Brazil back in any form is a plus. They might actually agree to allowing Brazil to be a self governing nation. Brazil, though, is more questionable. There is no doubt that they have to be made a full partner with full rights and say in the empire. anything less and they're splitting. They're going to want to rule themselves, and as OTL showed they weren't capable of doing so without some unifying force, which is why the regency period between Pedro I and Pedro II was a fiasco and why Pedro II was declared an adult at 14 (I think that's the age). They need a king, and Pedro I has no kids old enough to fit the bill. I think he loses Brazil, and I think Brazil splits apart. Under this TL, Paraguay under F Lopez actually has a chance of succeeding in the expansion game, and you could have a strong, if not dominant Paraguay develop. This all seriously alters Argentina's TL, as they suffer defeat to Paraguay, and/or break up themselves. Either could lead to no conquest of the desert (late 1870's OTL) by Argentina, and Chile takes control of the lower half of Argentina (which was their goal OTL-I believe they only gave up claims to avoid Argentina getting involved in the Chile/Bolivia/Peru war of early 1880's. with a weakened Argentina, this isn't a concern, and who knows what the stronger Paraguay does during that war. Probably uses the opportunity to take more land from Bolivia)