After Brazil (many ways for the Brazilian monarchy to survive), the most likely is probably Haiti, assuming post-independence PODs. But you'd need the king/emperor to be actually politically intelligent AND manage to avoid overthrow for him and his descendents. Some way to entrench monarchy in Haiti, basically, get one side of the country forever in favour of that sort of monarchy, even if the generals hold all the power and not the king/emperor himself.
Or just have a Bokassa-type situation in modern Haiti and have said dictator/wannabe emperor still be around in 2016. I definitely don't see any Latin American dictators crowning themselves--just wasn't in their culture to do so. And you could fill a book with the stories of bizarre dictators in that part of the world.
Mexico, well, Iturbide wasn't particularly worth much, and Maximilian accepting that title was like kicking a hornet's nest.
There were still some royalists politically active (as general conservatives) in the Latin American countries as late as the mid-19th century, including Gabriel García Moreno, Ecuadorian president. They mostly kept quiet about it and bowed to the political realities of their time. Any attempt to try and invite a Spanish royal to be king/queen wouldn't end well for them or their followers (and said Spanish royal is best off not even bothering going there).
For pre-independence, you have tons more choices. There were plans to find a suitable descendent of the Sapa Inca and crown him king/emperor, I think that was Argentina mostly but was discussed elsewhere. The Mexicans originally tried to get a Spanish royal to rule there, but Spain would have nothing to do with it and threatened other dynasties to not take up the offer either. There might've been movements elsewhere too along those lines. It seems as a whole you could probably get the Spanish monarchs to end up like the British monarchs in Canada and the Caribbean.