If it were me, and I really wanted honest answers, I'd contact someone
in the adventure tourism business in the area. Just a guess, but I
suspect there's a strong chance that the answer to your question will
eventually turn out to be "no" (firearms generally tend to be strictly
controlled in most of the world
This is an excellent idea. Just doing some digging around out of curiousity, it looks like Brazil has some very strict gun laws, a lengthy registration/permit process, a minimum age (25) and it's possible that it's not even legal for foreigners to carry within the country. That's not even taking in the possibility of penalization for shooting protected wildlife. It's a complicated, serious subject so a professional guide/adventure company familiar with local laws would be your best resource.
Cindy and Holly have provided some excellent advance as well! A guide service would ensure that your novice (assuming this is your first time) experience in the forest/jungle is the best one possible as, along with making sure you don't get lost, they can provide instruction on the things you DO need to be most cautious of, such as particularly harmful parasites and insects, and how to protect yourself.