From our experience I'd say that your chances for establishing a successful MFM triad vs a V are probably pretty good. It will all depend on how close you and your wife's tastes are in other people - personality, appearance, sexual preferences etc. If they are fairly close you probably will have little problem settling into a nice relationship. However - if your tastes vary widely - it's more likely you are going to end up in some sort of V configuration.
We (wife & I) of course prefer the triad and because our tastes are quite similar in both men & women and we learned how to be more open to little nuances that are more important to one than the other. The compersion thing. That's huge for both of us.
But to make a somewhat risky statement, we found that it's far far easier to find another guy that's truly open and reasonable about living in a relationship like this than it is to find a comparable woman. So if that's what you idealize we'd say your chances are good !
Good luck !