What if there is no Monroe Doctrine and Latin America is opened to European exploit? Argentina becomes a British Crown Colony, it finally achieves independence from Britain in the 1920's, but like Canada, Australia and New Zealand remains close to London. Assuming World War II isn't butterflied away, Argentina joins the UK in 1939.
By the 1950s, Argentina appears more independent than in years before the war, and has a very British style form of government. Like Canada and the US its an American nation made of immigrants with a British influenced government, becoming a two party democracy with incredibly high standards of living, and a stable economy. Argentina will be heavily industrialized in the north, while the south is mostly agricultural.
That would take care of the old Spanish power blocks. It would be intresting to see English surplant Spanish as the national language, but that doesnt really have to happen, maybe it will be like Canada, a bilingual nation.