Manuel A. Miranda was 8 when his family immigrated to New York from Bogotá. His parents, who had been lawyers, turned to selling home-cooked food from the trunk of their car. Manuel pitched in after school, grinding corn by hand for traditional Colombian flatbreads called arepas.

Today Mr. Miranda, 32, runs a family business with 16 employees, producing 10 million arepas a year in the Maspeth section of Queens. But the burst of Colombian immigration to the city has slowed; arepas customers are spreading through the suburbs, and competition for them is fierce. Now, he says, his eye is on a vast, untapped market: the rest of the country.

In the long run, like bagels, “you’re going to have arepas in every store,” predicted Mr. Miranda, whose innovations include a “toaster-friendly” version (square instead of round), and an experimental Web site that offers online sales nationwide. “But I don’t have the connections. I don’t know the people who can advise how to take us to the next level.”

As the flow of immigrants to suburban and small-town America outpaces the growth of bustling ethnic centers in New York, many foreign-born entrepreneurs like the Mirandas are facing an unfamiliar crossroads. In the city, rising rents and density hamper growth, while swelling ethnic enclaves in the suburbs generate competitors. Yet in other places, opportunity beckons as never before, as immigrants expand the tastes of mainstream America.