Given a choice, I would always pick the bike with the most progressive geometry. You can always put a set of light-weight fast-rolling tires on the Stoic if you want an XC feel. However, putting a set of aggressive tires on the Grand Canyon will not make it into a good trailbike because the geometry is jus too XC.
I suggest taking a test ride on the 29er Trek Roscoe and Marlin. Those bikes are similar to the Stoic and GC.