As far as Brazil goes, I think it could expand its trade with Canada if it wanted to. It really doesn't want to because it prefers to keep MERCOSUR whole. It doesn't want to see the MERCOSUR countries picked off one by one, by the United States or by Canada. They want to consolidate the bloc, and then the bloc may negotiate.
With respect to human rights, I'll leave it to someone else. I'm only an infrequent visitor there.