I found a really handy website for travel over at RFD, it's
http://matrix.itasoftware.com/cvg/dispatch/login
Just login as guest. You can do a month long search for various prices. Everything is in $CAD as long as you put YYC (or some other Cdn city as the "sales city"). All prices include all taxes and fees as far as I can tell.
To continue with the South American theme, I've found:
YYC to Panama City, Panama - $672 CAD
Late Aug until late Oct with Mexicana airlines. Although there is a overnight stay in Mexico City on the way there.
YYC to Rio $745 CAD
This is for pretty much everyday from Aug until mid November.
Same deal for YYC to Sao Paulo