Technically, the US and Brazil are presently neither allies nor enemies.
The US and Brazil were allies in World War II. Brazil was the only country to send troops to fight along side US troops. But there has been no formal alliance since then, which is to say there is no defense treaty between the US and Brazil in which the two countries agree to militarily defend one another if either is attacked. That is the definition of an ally. As such, the US and Brazil aren't allies.
As for enemies, the US and Brazil aren't that either. They are not in a state of war. The relationship between the US and Brazil isn't even characterized as hostile. There are a few points of tension, but that doesn't make two countries enemies. The US and the UK are extremely close allies, and there are points of tension between.
Where that leaves the US and Brazil is in neutral territory in which there is an ongoing diplomatic relationship between them. Now, some might argue that the US's Monroe Doctrine makes the US an ally of every country in the Western Hemisphere because it swears to defend any and every country in the Western Hemisphere from invasion by any country not in the Western Hemisphere, but there is no promise to reciprocate and some countries would rather the US butted out.