Preheat oven to 375 F.
Peel, core, and cut each apple into 3/4 inch thick wedges. Place the apple wedges in a large mixing bowl, and toss gently with the lemon juice to prevent discoloration. Peel the bananas, and slice them crosswise 3/4 inch thing. Add the bananas to the apples and toss to coat evenly with lemon juice. Sprinkle the cinnamon over the fruits and toss well to combine.
Melt butter in a large skillet over medium-high heat. Add the fruit and saute until tender, about 30 seconds. Add the brown sugar and maple syrup and cook until the sugar is dissolved, 30 seconds longer, remove from heat.
Pour the contents into a lightly buttered, non-reactive, 9- inch round baking dish. In a medium size bowl, beat the eggs, then stir in the milk and vanilla. Dip the bread slices into the egg mixture just to moisten (both sides), then place them over the fruit in a single layer in the pan, making sure to cover the fruit entirely. Pour any leftover egg mixture over the bread. Let the mixture sit for 10 minutes. (This can be prepared up to this point in advance, covered and refrigerated overnight)
Bake the French toast, uncovered until the top is golden, 30-35 minutes. Cool for 5 minutes. Place a serving tray over the pan, and carefully turn them over to unmold the French toast. Spoon any syrup or fruit left in the pan over the bread, and serve at once.