I agree that it doesn't have to be used every time, but the edit eliminated all use of the word 'Dominion' from the article. I think that the use of the title 'Dominion of Canada', to reflect the semi-independent federation of British territories that was Canada in 1885, just once is a good way to disambiguate the 1867-1931 use of 'Canada' from say 'Canada' as a colony in New France, The Province of Canada of 1841-1867, or even our current setup.