My understanding is that Canada bought enough doses to cover its population six times over - although, as you pointed out, its vaccination rate thus far is 65 doses per 100 (compared to 89 in the U.S.).
Mexico had been counting on an AstraZeneca deal (250 million doses total), whereby the active ingredient (virus DNA, etc.) would be made in Argentina and bottled in Mexico - but with some U.S. made ingredients.
And therein was the problem: there was an export restriction here in the U.S. until recently on most of said ingredients.
That left them dependent on other sources - though the AstraZeneca doses are finally now becoming available.
But Latin America still relies on China (Sinopharm and Sinovac, mostly) and Russia (Gamaleya) for most of their vaccines.
Even the two "star vaccinators" (Chile and Uruguay) are heavily reliant on Sinovac - despite having also signed with Pfizer (which can't deliver much due to U.S. export limits - for now).
So for all those reasons and more, Biden did the right - and smart - thing.
The announced numbers, though, are for now a pittance (6 million doses - when Latin America/Caribbean has 660 million people). That could change though.
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