Unlocked new IPhone

No, iPhones are not region locked per se, but make sure that the cellular band used in the US is supported in Brazil. Also, US iPhones don't feature a physical SIM card tray, So you can use these iPhones only with e sim

And also note: An iPhone purchased in the US, will have NO WARRANTY in Brazil, if you need warranty support.

If you live in Brazil, it's ALWAYS best to buy your phone where you live and will use it. Any cost savings you might find buying it in another country will evaporate and then some if you ever need warranty support.