I don’t really have a specific number of how many Americans, Canadians and other expats are living in Managua. That is a tough number to come across because there’s no census. Perhaps that is something that the US embassy could have a notion of.
I can say, from personal observation, that there are quite a few Americans, Canadians and other expats living in Managua. You see a lot of them in the streets. Most of the Americans living here in Managua (as opposed to other parts of Nicaragua) are businessmen, investors, and those who work at the Embassy. You have Americans working at the American Nicaraguan school or the Lincoln Academy (Lincoln International Academy). There’s a community here in Managua of expats who are mainly relatively young Americans of working age.
As for the expat retirees, I don’t think there are as many of them in Managua. They would be in other towns such as Granada or perhaps Leon (pictured) and San Juan del Sur and other destinations more known for tourism-- that’s where you will find the retirees.