Brazil is an enormous country. If you want to see it take a few weeks, and you will have a very diverse holiday.
The obvious starting point is Rio de Janeiro, with it's popular and beautiful Ipanema beach. Sao Paulo is a short flight away, it has no beach but great night life, most gay Brazilians live in Sao Paulo.
The holiday beach town for gay Brazilians Florianopolis. Visit Brasilia for it's modern architecture, Salvador for the beach, Iguazu for stunning waterfalls and make a tour in the Amazon from Manaus.