AeroMexico is having a good deal between Toronto to Buenos Aires, Rio de Janeiro, Lima, and Santiago de Chile. They’re going for $699CAD, which is a substantial discount on the typical $1200 fare.
There seems to be substantial availability throughout all of May 2015. Use ITA Matrix to search for availability, and then book
After finding your dates on ITA, use Kayak.com to search for your fare. This is a buggy fare, and doesn’t always show on AeroMexico, or if you try searching it directly on Expedia. However, if you go through Kayak, which will then direct you to Expedia, you’ll get the fare.
Thanks to OJ777 for pointing this out on RedFlagDeals.