You will notice the current two leading candidates are Greece and Russia.
But why?
It all comes down to this: It's not between Greece and Russia... this poll is between the Parthenon and St. Basil's Cathedral...
(if you want to include Australia and Egypt, it's also between the Sydney Opera House and the Giza Necropolis)....
Architecture.
I very much like your thinking here. Some great choices for icons (weenies) to build. However, you have to also take into account food, tourism to the areas, political climate and stability, obviously food, the countries willingness to help Disney find people to work at the pavilion, and what on earth would there to be to see and do inside of the attraction. I know that Disney had done some preliminary planning for a rollercoaster type of ride through for Russia when they were still pursuing that as a pavilion option. Remember, rollercoasters more or less started in Russia as mining trains. As long as it wasn't just a thrill ride, it could be a very nice attraction.
One thing I think that has been overlooked is the middle-east. Which would be why I would push for one pavilion from Turkey/Jordan/Egypt. (Pick one.)
Jordan has the temp Al Khazneh at Petra (used in Indiana Jones And The Last Crusade), Turkey has the temple Hagia Sophia in Istanbul, and Egypt I don't think I need to say much about as everyone else has already.
Anyway, so the keys to designing an attraction would include external architecture, something to see/do inside which could be movie, ride, museum, culture which is disimilar enough from both America/USA and other attractions already at EPCOT Center, and some sort of interesting food culture. Politically/economically Disney would want a stable country, one that won't draw lots of protests to EPCOT Center, a country willing to kick in some funding, also willing to help in recruiting students to work there, probably at least a couple companies willing to help in getting genuine trinkets there for sale, and of course chefs and restaurant people to help guide in restaurant setup and planning.
I am not that familiar with Brasil, so I'm not sure what sort of architecture and what sort of history Brasil may have to offer for either a museum or ride of sorts. But so far, Greece, Russia, India, Egypt, Jordan, Turkey and Australia/New Zealand all sound like great ideas to me. Diversity would be a key to this too.