To answer the question as to why CAE for the 7X, I have been told that CAE has more experience with developing training programs for fly by wire aircraft. Having been a long time FSI client, recently I attended Simuflite for the first time and was surprised at the increased level of professionalism over FSI. Yeah, a sim is a sim, however, having attended 4 different FSI facilities over the years it is nice to work with instructors who love who they work for in addition attending a modern facility. The training costs of 1/3 less than FSI are great perk too.
As far as Dallas being the training center for the 7X, I also heard that CAE will be building a new facility on the east coast for this program and others.