Immigrants have always done that in big cities, long before the word multiculturalism came into usage.

This excerpt from wikipedia is just one example:
"Italians arrived in Toronto in large numbers during the early 20th century. Italians first settled in an area then known as The Ward, centred on University Avenue and College Street. By the 1920s, most Italians had moved west of Bathurst Street and the College-Clinton area had emerged as the city's major Little Italy. The affordable Edwardian homes that line the side streets of this neighbourhood were bought by Italian immigrants, many of whom found work on the railways and in road construction. Italians started businesses on and around College Street.".  

It may take a couple of generations for different immigrant groups to enter the mainstream - but it happens.