Well it also depends on the overall way colonizers go about colonizing the Americas; and if there is the cultural space for such mixed peoples to develop into a distinct identity. Latin American Mestizos came about as a result of Spain not so much as creating settler colonies, but more of an idea of using the existing population to exploit needed resources such colonies offered (somewhat like Africa and Asian colonies). Race as we think of it didn't exist so much as a concept either. It was more about the fact the Natives weren't Christian, which gave the colonizers the excuse to dehumanize the Indians. Mestizo as an identity came about not only because of mixing between the Spanish and Natives, but as a way to divide and conquer the indigenous. It was like saying 'your almost human enough to hang with us', thus giving a group a little bit of privileged over another; which is why in Latin America of today, Mestizo means more then just a mixed heritage, but includes 'full-blooded' Indians who've adopted western clothing and culture.
Now the Metis of Canada came about as a truly distinct culture, as they merged the cultures of both their parents and thus becoming a separate ethnic group. This is a far cry from say someone who is mixed back then or today, who is mixed, but identifies with either or all of their heritages.