This is what I have so far for a crossover idea of AC3 and Hetalia, since its related to the American Revolutionary War. I do actually have this urge to write fanfiction on Connor's interactions with Alfred before, during, and after the war but I can't seem to write it out.
I see Connor meeting Al numerous times throughout his life such as meeting through America's future-1st-boss and during the battles. It may be un-accurate depending on what age/appearance America takes on during his development as a colony-then-nation from being a "newly discovered land". Also AC3 does not even release until this fall because Connor's full story has not been revealed yet.
I have reserved the game to play the experience myself.
But in the mean time, it is possible to write one about Prussia and Altair as well as Chibitalia (and Romano) with Ezio since AC,AC2,ACB and ACR are already out. Though it also possible to put Prussia, England, France, Canada, and Spain with AC3 because of the colonies in North America, too.