AFAIK the DL ATL-EZE flight is daily year round. Some of the GIG/GRU flights are not, such as DTW-GRU that operated about twice a week when I used it. There are also daily AR nonstop from JFK to EZE, but they don't seem to be codeshare. I don't know whether AR serves other USA locations and I don't know what the GOL routes are from the USA either.

AA seems to have lots more flights to EZE and other South American airports than DL does, not only through MIA but also using some other AA hubs.