The ones I can think of for myself are pretty small-scale beliefs, but amusing! As a child growing up in British Columbia, which Canadians consistently shorten to "BC," I was used to "BC" in abbreviations and acronyms standing for British Columbia. That's true for things like BCAA (the BC branch of the AAA/CAA) and ICBC (the crown corporation that insures all cars in BC), but not so true for CBC, the Canadian Broadcasting Corporation. I thought that every province had their own province-specific name for their public radio station (I mainly encountered CBC through radio)!

It also took me a long time to figure out that the Saint Lawrence River flowed out of the Great Lakes, not into them.