The term 'dominion' was adopted in 1867, when Canada formed its federation, so is its modern moniker, after the 1982 Canada Act, a 'dominion' or 'confederation'? (even though it is technically a federation, not a confederation)
While the term 'dominion' is mentioned in the BNA 1867 and Canada was frequently referred to as the 'Dominion of Canada' the designation dominion was not entirely official. Over the years as Canada's attachment to the British Empire lessened the term 'Dominion' fell out of favour and Canada became simply referred to as Canada.
Although if you want a technical answer on the form of government Canada is. Since 1867 Canada has remained a federation of provinces despite shifts in the power dynamic between the central government and provincial level over the years