While we carry a firearm on the the occasions that we go up into the more remote areas of BC, we are in compliance with Canadian regulations.
I would suggest finding out what the firearm requirements in Brazil and the other countries you are going to pass through are--- if you don't already know--- and then complying with them. We travel all over the world in the course of our Boeing jobs and while we are not dealing with firearms regulations we are dealing with customs and security officials on each trip with regards to our video equipment, and believe me they can be incredibly thorough and determined in their investigations and regulation enforcement if they choose to be. If they for whatever reason think you may be concealing something they will move heaven and earth to find it, and they eventually will.
A firearm is a lot more serious thing than a video camera, even a $100k camera like the ones we bring into the countries we visit. Given the risk involved in being caught in non-compliance with the governments of other countries and the potential penalties it's not something I would want to risk.
I certainly understand the concerns you've expressed and the initial reaction could well be to have a firearm for protection on board. What you have to do is balance that against is the potential risk to you and your boat if you're discovered to be in non-compliance with the firearms laws of each country.
I guess the way I would approach it, given my experience with the thoroughness of other nations' government agencies and inspectors and the seriousness with which they take foreigners' compliance with their regulations, is that if I really felt I needed to be armed to be safe while boating through these countries, and if the laws prohibited me from being armed, I would go boating somewhere else. Either a place where being armed is not something I felt I needed to be, or a country where being armed was allowed.
It's a decision only you can make, however. As Clint Eastwood would say, "Do you feel lucky?"
