I am not claiming that the United States has most of the world's cardinals; I am claiming that it has most of the cardinals that are in anglophonic nations, which is relevant for the Anglophonic article.  In a Portuguese-language article, the appropriate dialect would likewise be Brazilian — not because Portugal does not matter (not being the mighty Brazil), but because Brazil's the Portuguese-speaking nation with the most cardinals.  If you'll accept this natural metric, then I'll bother to get you the population estimates; otherwise its a bit of a goose chase for me (and this article is not on geese).  But you, as a birder, should know enough from considerations of habitat. —