I'm not sure of the figures but in Canada and the U.S. it seems like the Native population was almost completely replaced by Europeans, Africans, and other immigrants, whereas South of the border that doesn't seem to be the case.
More answers and discussion are always welcome, but check out this section of the FAQ:
Why are there a lot more Native (and native-mixed) people in South America than in North America?
Why did Natives mix with Europeans in Mexico but not as much in the United States/Thirteen Colonies?