Nobody is sure if it is suicide or not. Ghazi was to the Lebanese what the High Commissioner was during the French Mandate. link. The body of Ali Kena'an was found crushed by a train, so this one is more easier to judge as murder rather suicide, but it is never 100% known.
In Lebanon last year, when we heard Ghazi Kena'an committed suicide, a joke spread that "General Ghazi committed suicide by shooting himself three bullets in the back."