Will an US purchased Mac receive Warranty coverage while in Brazil?
TL;DR - Yes, the warranty is international, but you may have to pay shipping and wait longer for service if Apple USA can't find a local provider and/or you can't find a local provider for service while in Brasil.



What holds true is an owner always can contact AppleCare for the country in which the Mac was first sold. In this case, a web query or phone call to the US offices of AppleCare are your best options from Brasil unless you can find a local service provider that will honor Apple's US warranty.

Most of the time, Apple providers get paid enough and are happy to get reimbursed directly from Apple and can rapidly determine warranty coverage from your serial number, but that's really up to each local service provider to decide if and when they will do the work to accept a cross-border repair.
I can't make a blanket statement that all will say no or yes since it'll be somewhere in the middle most of the time. 

Check here for worldwide options - https://locate.apple.com/country and here for options within Brasil - https://locate.apple.com/br/pt/