This isn't really about what countries were supposed to be, but you asked for EPCOT trivia, so here goes!
Initially, EPCOT was supposed to be a living breathing Experimental Prototype Community Of Tommorrow. Tons of info on that at
www.waltopia.com
Anyway, when that went south, there were different ideas for how to create a theme park out of that concept - and among the themes that were being created were a park about the future, and a park with pavilions representing different countries - a standing world's fair concept.
The Imagineers had eyed land between the Contemporary and Ticket and Transportation Center to build this park - and what they had planned to do was to solicit coporate sponsorship from the countries. The size of each pavilion would be determined by the amount of money that a country could provide to fund its pavilion.
BUT, what the Imagineers decided to do - to avoid any flashy spectacle for any one country - was make the facades non-descript, and exactly alike in size and scope. Think of the entrance to the current Mexican pavilion - passing through a door and then behind a wall - but without the lavish Mayan pyramid - just a stark white design with perhaps the name, flag, and colors of each country visible.
The INTERIOR of the pavilion could then be huge if a large sponsorship was given, or smaller if a smaller sponsorship was given.
But all that went south when the Future park concept and the World's Fair park concept were pushed together to create what we now know as Epcot.
If I can find the link to the original story where I read all of this, I will. But my computer crashed, and I lost my links.