Preheat oven to 300 degrees F (150 degrees C). Grease four 7x3-inch loaf pans.
Mix 1/4 cup sucralose sugar substitute and 1 teaspoon cinnamon together in a bowl. Dust the prepared loaf pans with sugar-cinnamon mixture.
Beat margarine and 1 1/2 cups sucralose blend for baking together in a bowl using an electric mixer until smooth and creamy. Mix bananas, egg substitute, sour cream, vanilla extract, and 2 teaspoons cinnamon into creamed margarine mixture until smooth. Stir flour, protein powder, baking soda, and salt substitute into banana mixture until batter is just mixed; fold in walnuts. Pour batter into the prepared loaf pans.
Bake in the preheated oven until a toothpick inserted in the center of a loaf comes out clean, about 1 hour.
