Honestly, I have always thought of the Breen as more in keeping with an eventual Cardassian or Dominion faction (I am still holding out hope that they are two seperate things).

Probably more Dominion then Cardassian, not sure the Cardies like them very much anymore with the whole Dominion war thing, but I suppose arguements can be made for either side.

To me I can only see the Breen ally with anyone. If they have a goal in mind and can be met with the Alliance. Similar how they did with the Dominion. The way the Founder told the Breen General she will give him all kinds of planets. As long they help win the war. And later while loosing, he was not in favor of retreating to regroup. Showing they are Klingon like in battle. Battle to the Death. Even the game shows this in a way with the story line.

I wouldn't mind seeing more story with the Breen in the future. Either as a "bad guy" or ally to help out a bigger threat. After they saw they are loosing the fight.