RGB: Brazil might attempt some movements up north, in the European controlled Guyanas, but they probably can't do much else. The CSA will be far too concerned with fighting the United States. However, should the pro-British Argentina enter the war, things might heat up...
stnylan: It's certainly possible. Living in a place for a long time does tend to make you affectionate towards it. For now, however, Adalbert does his duties for Germany. Brazil is merely a pawn on the giant chess board of the Great War.
Fulcrumvale: In this timeline, the Carribean is pretty much a Confederate lake. They own Cuba and have several naval bases in the Carribean colonies of their British and French allies. The Carribean flotilla of the navy would be quite threatening to Brazil, but I would think the CSA would be more concerned with the USA. War with Brazil would be symbolic at best.
Britain can probably project some power into Brazil, but not much. British troops certainly won't be landing in Rio de Janeiro. However, a substancial part of Brazilian trade is carried by the British merchant marine. If anything, Britain will seek to bleed Brazil economically, but stopping imports (which it depeserately needs--they have bare industries, after all.)
Brazil, however, does not exist as an ally to project her power. She is an ally for her resources. She can provide Germany with rubber and an array of food stuffs and resources to produce industrial goods, which may come under strain should Britain establish a blockade over Germany. Germany will milk Brazil for what she's worth.