The occasion marks the joining of the British North American colonies of Nova Scotia, New Brunswick, and the Province of Canada into a federation of four provinces (the Province of Canada being divided, in the process, into Ontario and Quebec) on 1 July 1867. Although Canada is regarded as having become a kingdom in its own right on that date, the British Parliament kept limited rights of political control over the new country that were shed by stages over the years until the last vestiges were surrendered in 1982 when the Constitution Act patriated the Canadian constitution.
So July 1 is a declaration of federation with a declaration of independence chaser and a 100 year mortgage. What I find interesting is the long arm of the British Parliament. Not that there's anything wrong with it.
To all who celebrate this weekend, enjoy your hot dogs (vegetarian in this household), cherry pie, nanaimo bars, and Henry Gibson (yes, that one) performing 200 Years from the Nashville soundtrack.