Thirteen percent of the US population is foreign born.
Twenty-eight and a half percent of Australians is foreign born.
Nineteen percent of Canada is foreign born.
The majority of all these countries are native born! Hence none are "nations of immigrants"!
And the people who settled these countries weren't immigrants either. How? Well, in order for people to be immigrants, there needs to be countries to where they go. America wasn't in existence until people settled it. The founders simply went to a land mass with no existing nation. They made one.