Alright. We don't want to squish everything, so here we go. Everything matches the Canon as set forth by the games and the books, but game canon take precedent. And we tend to ignore those books. You know the ones. The ones with Kai Leng stealing Cereal. Everything after Mass Effect follows thusly. Shepard's Gender/Love interest is to be left ambiguous (Despite a certain Quarian being best choice) and the ending here is Destroy, with a twist. The Geth were spared, and the Mass Relays were fixed within a year.
And if anyone mentions a starchild. I swear to Amonkira...