it's a dog with good temperament.not sure about the climate stuff.training should not be a problem.Well I checked profile of Bullmastiff but its not very much adaptable towards hot climate. Moreover its training is also not very easy.
avoid all aggresive ones.GSD or doberman are nice but might run out of patience. lab is much preferable that way.
how about the dalmatian, even danes? not much idea about these two breeds.