Because of the current aviation crisis caused by the Covid 19 virus crisis, all Airlines have canceled a large number of flights.
Particularly the international routes have been impacted, with some Airlines like American Airlines cancelling all service to some countries. Brazil for example right now has no service from American Airlines, which has left thousands of angry passengers stranded on many countries and scrambling to find their way back home.
In the case of flights between United states and Brazil, these are the carriers which still have non stop service oporating.
LATAM Brazilian Airlines: Still flying from Miami and New York to Sao Paulo, Brazil
Azul Linha Aéreas: Still flying from Fort Lauderdale and Orlando to Campinas, Sao Paulo.
United Airlines: Still flying from Houston to Sao Paulo and From Washington , DC to Sao Paulo.