Preheat the oven to 350 degrees F (175 degrees C). Grease and flour a 9x13-inch baking pan.

Whisk 1 1/2 cups sucralose sweetener, milk, 3/4 cup melted butter, eggs, and vanilla together in a large bowl. Whisk 3 cups flour and baking powder together; stir into milk mixture until just blended. Fold in blueberries. Spread evenly in the prepared pan.

Combine malitol sweetener, remaining 3/4 cup flour, and cinnamon in a small bowl; stir in 1/2 cup softened butter with a fork until mixture is crumbly. Sprinkle over top of cake.

Bake in the preheated oven until a toothpick inserted into the center comes out clean, 35 to 40 minutes. This cake is best served warm.