While the Overseas areas of France are considered part of the Metropole today, they were'nt originally, though France is really the only European colonial power that could be compared since it did actually attempt to integrate its colonies as part of the Metropole.
There is a very substantial difference; the European colonies were established not to expand the land area, but as a mixture of economic exploitation and strategic need; in the U.S. expansion was done to incorporate new lands as direct and equal parts of the country and exploitation in them would be no different than it was in the traditional Metropole.
Still colonizing someone else's land, still a brand of imperialism. You also seem to be forgetting the examples of the Louisiana Purchase, Hawaii, Alaska, Puerto Rico, American Samoa and the Phillipines, all taken as a mixture of economic exploitation and strategic need.
And Britain considered their citizens in the Americas to be just that, citizens. Until they lost that pesky little rebellion, that is.
