Both Varig and TAM offer airpasses. You might consider buying a cheap OW GRU-GIG after you arrive in the local currency. SHouldn't be any problem as ther are many flights but you may go to the Santos Dumont airport which is closer to the beach than GIG.
THe Brasilia/Manaus might be accomplished by an award ticket on Varig or TAM (from AA) that allows a stop in Brasilia to or from Manaus