Currently, the Mercosur countries (Argentina, Paraguay, Uruguay and Brazil) do no have any treaties with the USA -- tax or otherwise. And they are loudly not interested in becoming involved with any trade treaties with the USA. However, the easiest way to become an Argentine Citizen is simply fill out an application to legally open and operate a business with a minimum of U$S49,000. Triple that (actually Argentine Pesos are 3.4 to the U$S Dollar at the moment -- prior to 2001 one Peso equaled one Dollar) and you have enough cash to open any number of small businesses that actually generate a good living in Buenos Aires, a city with the densest population in which I've ever lived. Of course, you had better be fluent in Spanish and ready to bribe public employees to push your paperwork through. I have thought about opening a gay pub -- a "resto bar" open for business in the gay-ish neighborhood around the part of Avenida Santa Fe that encompasses the barrios of Recoleta, Barrio Norte, and Palermo. But a nice Russian guy and his boyfriend opened a similar place 4 years ago called Flux, and are barely scrimping by. Part of of their lack of success is due to their location, but porteños simply have no old custom of havinig drinks after work. Instead, they go home, eat, hang with their boyfriends/families, and then go out for coffee at 10:00 PM until the dance/cruise bars open at midnight. But there are many other small businesses that I would have never considered viable that generate an amazing income, such as Maxikioskos -- basically, a candy and cigarette store where you can buy a Coke, make a phone call from a phone booth, have photocopies made, sell an ice cream bar, and prepaid telephone cards. However, Buenos Aires is currently suffering a lack of coins crisis. Inflation has risen just enough that taxis, buses, and the subway require a range of exact fare in coins that it's almost impossible to get change, thus folks hoard it for public transport. That makes buying candy bars and making change for hundreds of customers all day long almost impossible.
One can apply for and do something similar to get a foot in the door in Canada. However, the cost is much higher and you must present a business plan that ensures you will create 6 new jobs for Canadians and have enough money to keep your business afloat for 3 or 5 years (I forget the actual number of years). It was something that I was actually looking into two years ago. My mining services business would have easily qualified and more than likely flourisehd if I had been willing to set up shop in northern Alberta -- way north, as in around and about the kimberlite mine far north of Edmonton. Sadly, owning a coffee shop in Kelowna (I love that area of BC) would probably fail due to all of the coffee shops that are currently competing for the same business from a finite population.
But Uruguay has a very small population concentrated mostly in and aroung Montevideo. The most stunning beach property with ultra modern glass and steel homes that seem to float above the ground can be found on the road out of Montevideo to Punte del Este. And 100 million dollar+ private yachts that can sail to any port in the world are very common. So, Uruguay is definitely up to something regarding is liberal banking laws. Those same yachts never make it up the Rio del Plata to Buenos Aires, because the economy is too unstable. Uruguay had some troubles in 2001 when Argentines could no longer afford to show up en masse for January and February vacations, but that's ancient history in Montevideo. All one needs to open a bank account is show your passport and designate what amounts to a post office box as your address. There is an official law that no one can enter the country with more the U$S10,000 in cash in their wallet, but that's a USA law agreed by treaty which Uruguayans are more than happy to overlook. A good portion of Uruguayan society makes its living buying and trading world currencies. Again, you need a solid grasp of Spanish and the ability to decipher the Rioplatense dialect spoken by both Uruguayans and Argentines -- which at times can drive you crazy. They speak funny down here.