Today is my country’s 143rd birthday. Yay!
Canada Day celebrates the enactment of the British North America Act, which, on 1 July 1867, united the two British North American territories of Nova Scotia and New Brunswick (which they stole from the French about 100 years prior in Le Grand Derangement — see my lesson on the Acadians) and the provinces of Upper and Lower Canada into one big dominion of Canada.*
The holiday became a statutory holiday in 1879 and was called Dominion Day until 1982, which, not coincidentally, was when the Canada Act was signed.
As a side note, apparently Quebec has its own holiday on 24 June.**
*Minus Newfoundland, which wasn’t a province until 1949.