At probably around the same rate Americans and Canadians are lumped together in India, that is, until you get to know them or they give some clear indication (flag, etc.)
I think Australians and New Zealanders get the same, confused for each other. And us Dutch are confused a lot with Germans too. Not that I wear a flag for it though :)
Source: Shared a house with a bunch of Canadians :)
And I am German.