Raises a unit synonymous with power of leader in North American capital (6)

I believe the answer is:

ottawa

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'north american capital' is the definition.
(capital of Canada)

I cannot understand how the rest of the clue works.

(Other definitions for ottawa that I've seen before include "North American city" , "Canadian city" , "Canada's capital" , "capital city" , "N. American city" .)

I've seen this clue in The Irish Times.

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