As a Canadian I can answer "What's Canada Day all aboot?"
It is really quite simple. It's about sneaking in a long weekend just before the US. We did the same thing with Thanksgiving, since ours is in October.
It has the added benefit that even though we are all at work today, all our customers (Americans) and/or head offices are off, so we get to sit around
Historians will tell you its really when Canada become a Dominion in 1867 (a step up from colony, but not quite a country), but thats all lies.