I believe the poster is traveling to SA South Africa, and not South America.
The good advice given above still stands, but the high volume of one is quite different from the other. South Africa will be far from the volumes of Argentina, specially if combining a big game and wingshooting trip.
Regarding choice of gun for doves in Argentina, it goes down to personal preferences, and in this, I include the kind of cover you are shooting.
IMO, The great thing about Argentina dove hunts, is the variety of places where you can shoot them.
You can snap shoot all day in heavy cover where skeet&skeet would be perfect, or go for something a bit higher,or much higher , shooting from the valleys or in the flyways in open ground to and from the roost.
Again IMO, break action guns are always better, as they are easier to load and present fewer problems.
Sometimes the loads leave so much residue, that auto's begin to jam after 3 or 4 boxes.
Absolutely no reason to take a 12 gauge, 20 is good 28 is even better !!