Like any good friend, Thomas Jefferson wrote back to James Monroe when asked his opinion on the proposed alliance with Britain to protect Latin America. Although he couches his thoughts by reminding Monroe that he has been so out of the political realm that he is "not qualified to offer opinions on them worthy of any attention," he still gives some pretty strong arguments in favor of accepting the proposed alliance. (Source)

Yep, Jefferson supported Canning's proposal, and tells Monroe as much in this letter. One of his biggest arguments is that having Britain as an ally would empower America by giving the country the ability to protect the western hemisphere. He says:

Great Britain is the nation which can do us the most harm of any one, or all on earth; and with her on our side we need not fear the whole world. (Source)

Jefferson makes some other points, though, that can be seen in the text of the Monroe Doctrine and its legacy. He tells Monroe that the U.S. should never get mixed up in Europe's affairs, which is one of the main points of Monroe's speech.

Jefferson also wonders, pretty casually, if the U.S. hadn't thought about taking some of Spain's former possessions for its own. He seems to have a special fondness for Cuba, although specifically points out that it's not worth going to war over.

Just, you know, if it happens to go on sale, it's something to think about.