There have been several stages in the history of Canadian independence.
Canada became a self-governing dominion within the British empire on 1 July 1867 when the British North America Act was passed by the UK Parliament in 1867.
The Statute of Westminster, passed by the UK Parliament in 1931, acknowledged Canada as co-equal with the United Kingdom within the British Commonwealth.
Canada obtained full autonomy when the UK Parliament passed the Canada Act 1982 in 1982. This granted full sovereignty to Canada, and so marks the date at which Canada became truly independent.