Australia VS Easter Islands
This section is actually more a joke then other, had to add it after I found out that while in the movie Bunnymund's warren is under Australia, where it's said that spring is born in that continent; the Book version of Bunnymund has it's warren under Easter Islands, which I think is quite appropriate, giving the name of the islands.
While in the book, he doesn't live under Australia, still, Bunnymund's favorite continent stays the Aussie home.
Earth was originally egg-shaped, but that was rotationally unstable, so we were heading toward the sun. The planet was going to be cooked like a hard boiled egg, so against his aesthetic judgment, with his incredible digging ability, he rounded out the Earth into a rotationally more docile sphere. In doing so, he created a number of continents, among them his favorite, Australia - W. Joyce
Theory is that in the movie Rise of The Guardians they gave to every character a continent or at least somehow the continent, and tried to show it thru the personality and/or how they dress and where they live. For example: Jack represents North America, his home is in North America. Toothiana represents Asia, look at her how she is dressed and where she lives, even before knowing, it gave me India vibes. North is Russian, and not just because of his accent, he is known for being a Kosack and also his clothes point in that direction. So, with the fact that Bunnymund's favorite continent in the book is Australia, it's normal that Bunnymund became an Aussie. He has Australian accent, maybe he doesn't have clothes, but I think those boomerangs are all we need to know which continent he belongs too. Now that makes me question if Sandy represents Africa.