I do not think that there is a word with more spelling confusion than Iguaçu. The possibilities are: Iguaçu (Brazil,France), Iguazú (Argentina) Iguassu (English, international, airlines’ lingo), Yguazu, (Paraguay). You will probably see in touristy material something like “The Iguassu Area” – in an attempt to include the three sides of the Triple Border. Iguassu is supposed not to be Brazil, Argentina or Paraguay. But this attempt does not go very far either. That is the Brazilian proposal or putting better, the proposal of the “IguaSSu Right”. This subject was never offered to the consideration of Paraguayans and Argentineans. What we do have and was achieved by Mercosul*/ Mercosur's Resolution 41/97 is the Polo Turístico Internacional Iguaçu / Iguazu (PTII) which would roughly translate as The Iguassu International Tourism Pole – one of the first Community- Integrated Tourism Product, community here in the Mercosul, EU sense. What it really means, is that there would some kind of cooperation in matters like visas, tour facilitation and so on.
If you are a citizen of a country that needs a visa for one of the three countries of the Tourism Pole, you would have free access to all the attractions of the other two countries on the border if you have been legally admited to one of the three countries. Have I made myself clear? No?! Today, if you are in Puerto Iguazu, Argentina, you a need a visa for Brazil and want to see the Falls on the Brazilian side, you will probably be turned down. The Tourism Pole has a physical area. It can be seen as circle around the Foz do Iguaçu, Puerto Iguazú, Ciudad del Este and two other Paraguiayan places - one of them where the Airport is. You can't go beyond that circle. Argentina already has a checkpoint about 50 kilometers from the borderline equipped with soldiers, sniffing dogs and so on for the purpose of sending offenders back to Iguazú - on the border. And they do!
*Mercosul (Portuguese) or Mercosur (Spanish) stands for Common Market of the South brought into existence by the Treaty of Asuncion.