In a saute pan, melt 2 tablespoons of the butter. Add the pecans and saute for 4 to 5 minutes, stirring constantly. Stir in the maple syrup and bring the liquid up to a simmer. Remove the pan from the stove and add the rum. Carefully place the pan back on the stove and flame the sauce. Remove the sauce from the heat and set aside. In a mixing bowl, whisk the eggs, milk, sugar, cinnamon, and vanilla, to dissolve the sugar. In a nonstick saute pan, heat 2 tablespoons of butter. Dip 2 slices of the bread into the egg-milk mixture, coating evenly. Fry in the butter until golden brown, 2 to 3 minutes on each side. Repeat until all the butter and bread is used. Lay the pain perdu on a platter. Slice the bananas into 1/4-inch slices. Pile the bananas in the center of the pain perdu. Spoon the warm sauce over the bananas and pain perdu. Dust the entire plate with powdered sugar.