I flew CO TPA-IAH-GRU in August 2001 to attend a meeting outside of Sao Paulo. (I arrived one day late because CO couldn't get me out of TPA in time to make the cnx in IAH, but that's another story.)

I had a few free days after my meeting, and I wanted to extend the trip to EZE. A very helpful CO agent checked possible routings, including returning EZE-PTY-IAH-TPA and EZE-PTY-MIA-TPA, but we finally concluded that the best choice was to do the TPA-IAH-GRU r-t on CO and then buy a r-t ticket between GRU-EZE. I flew TAM and was extremely happy with their service on the 2 1/2 hour flight, with beverage service, meal, and post-meal coffee or tea.

Because you (apparently) don't have a reason to be in or near GRU, this may not be the best routing for you. However, given the EQM rules on CO, you are probably best off flying CO as far as you can and then going on to EZE.

Incidentally, CO did have plans to start serving EZE in fall 2001. In fact, EZE was shown as a future destination in the CO in-flight magazine as late as March/April 2001, I believe. When I asked the CO agent about it when I purchased the ticket to EZE, she told me that the economic problems in Argentina made CO decide to back out.

As Jaimito Cartero noted, GRU is not the most connection-friendly airport in the world. If you decide to transit through there, give yourself plenty of time to connect both ways. There's not much to do at the GRU airport, but outside of immigration, there's a McDonald's, a few small souvenir shops, and a coffee shop that will sell bags of its delicious whole-bean coffee.