Pre heat oven to 350 degrees. Prepare an 8x8 inch pan with cooking spray and dust lightly with flour. Place blueberries in a strainer and sprinkle with a T of flour. Shake out excess flour. This coating will prevent the blueberries from sinking to the bottom of the cake. Set berries aside.
I like to prepare the topping first. In small bowl combine all crumble/topping ingredients and set aside. In mid size bowl combine dry ingredients and whip with a whisk to incorporate. Set aside.
In large bowl, with hand mixer combine butter, canola oil and Splenda and mix until smooth, about 2-3 minutes. Add eggs one at a time and mix, then add vanilla, sour cream and half and half. Combine well. Add the dry ingredients to the wet in two batches, scraping down the sides of the bowl as you go and mix until smooth.
Fold in blueberries and pour batter into prepared pan. Sprinkle the prepared topping on the cake and press down lightly with your clean hands to make it stick to the batter. Bake 35-40 minutes and remove to cooling rack. Let cool at least 30 minutes before you dig in. Slice into 9 portions.