Looking for a hard tail mountain bike in the $1500 range. Is Trek, Specialized, or Cannondale the way to go?
Quite frankly, the brand matters very little when it comes down to the bets bike. Trek, Specialized and Cannondale are all great brands with great bikes, but your best bet to finding the right bike is to test ride them.
All of the brands you mentioned build good strong bikes, I would recommend either of the three. I, personally, ride a Specialized and have been very pleased with it for about 3 years now.