Every major city in the U.S. seems to have some large minority or ethnic population that is relatively unique to that particular area
Not really, nearly all unique immigrant population's are located on the coast's and very rarely will you find a population in the middle of the country that is unique to the country as a whole.
(and Brazilians and Carribean populations for that matter) do not self identify themselves as black or even hispanic.
Brazilians are not hispanic, because they speak portuguese. Also many immigrants from latin america are mixed white, black, ameridian and some are of asian ancestry.
Further, although we have a significant amount of foreign born blacks, including but not limited to Hatians, there are larger communities in NYC and Miami
true but Boston has many more african immigrants.