The best way to find a friend for you guys is to take them down to the shelter and have them meet several bunnies there. They will pretty much pick their friend for you - there will be a bunny that they ignore or take to right away - that's the bun to get if you want to have a good shot at bonding.
The personalities are important, but having them meet several bunnies will likely work out best.
Also, introducing a 3rd bunny is always a risk. You may break an existing bond or it might go well, there is no real way to tell until you do it, but having the buns meet other guys is the best way to get a good idea before you bring someone home.
Nadia