The way I play it, I combine the two rivers plus GQ11 tiles (removing the extra source tile), and build the City first.
If you have both River expansions and GQ11, then there are three tiles that have a river through the center and city on two sides. Conveniently, one of those tiles is the bridge tile that makes the same city on both sides. That means you can have the river flow *through* the city of Carcassone. Split the city in half, start with those three river pieces as the starting point and then just play with the river able to grow in both directions.