[Quiet Man Cometh]

Okay, this: "it celebrates the anniversary of the July 1, 1867, the effective date of the Constitution Act, 1867 (then called the British North America Act, 1867), which united the three separate colonies of the Province of Canada, Nova Scotia and New Brunswick into a single Dominion within the British Empire called Canada."

So not technically a "birthday" but one of those good-enough things. Apparently we weren't technically a fully independent county until 1982. By then, it was probably one of those things that people just never get around to doing because it's more a formality than anything.