Because it takes place at almost the same time and you even have the Hessian in the game as well (the bridge next to where you find him looks almost exactly like the one in the movie, no way that's a coincidence).

I think it might be amusing if either the characters stumbled into each others' universes or met (doesn't have to be both; Connor inverstigating the Headless Horseman instead of or alongside Crane, getting fed up with the incompetence surrounding him and going off reading clues on his own, a completely different plot, anything). Throwing Haytham into the mix would be funny as well.
Super bonus points for an idea that is totally random: Because side characters are great and I really liked him and was amused by his description in the Database, Mason being included and writing a completely over the top story about what happens would be gold. But it's just a random thought and not necessary at all!

Either Gen (canon movie pairing is fine, too), but if you want any pairing with Connor, slash only, please (I'm not picky).