I just thought of an interesting question pertaining to Vivillon.
If you have an existing save, and change the region on your 3DS (and let's be honest, this can randomly happen if you move across country, and I think both Canada and the U.S. have different types around each country; I know Canada has two), will that change affect the EXISTING save file? Or would you be forced to create a new file to get the new Vivillon?
The question came to mind as I mused about changing the region for Animal Crossing. The same question came up in my mind for that as I was musing, then Vivillon entered my mind.
If anyone is willing to test this (so I don't ruin my own game, I'm a completionist and don't want that hard work gone to waste), I'll be happy to trade a Polar Vivillon's Scatterbug Egg for an Egg created after a change. I'll then hatch it and keep it alongside me with the Exp Share active, and report back to you what type it ends up being (and don't tell me what your type is or the region you set to). This way we can properly test this guess. :)
If it works, I'll be setting up a Scatterbug trading shop in my PC.