January is a really busy time in Rio because of the Rio Carnival that has become world-famous through the Samba Parade, a show, display and competition of the Rio samba schools. So I would suggest to book ahead if you can. Iguazú Falls is undoubtedly the most visited place in Misiones and one of the most imposing natural attractions in Argentina.
I believe it is one of the most spectacular sights in the world.
You may want to take a look here:
Iguazu Falls.
The falls can be seen up close (plan to get wet) by walking along the upper and lower "circuits" of the walkways.
Both are well worth traversing.
To explore & experience Brazil's stunning natural beauty you can look here
Brazil Tours.
You said you want to see the wild life, Pantanal could be the place for that, an immense wetland area famed for its abundant wildlife.
Marvel at macaws, Jabiru storks, giant otters, anteaters, caimans and countless other species of fauna.
Pantanal .
And also for things you can do in Rio I suggest you look at
Things to do in Brazil. Enjoy your trip, I'm sure Rio will take your breath away!