Coat slow cooker bowl with nonstick cooking spray.
In medium-size bowl, whisk together the flour, pudding mix, sugar, baking powder and salt. Make a well in the center and add milk, canola oil and vanilla. Gently stir until batter is smooth. Stir in butterscotch chips. Pour evenly into slow cooker bowl.
In a small bowl, stir the butterscotch sauce and the sugar together; pour in 1 1/3 cups boiling water and stir until smooth. Pour over batter in slow cooker. Cover and cook on HIGH for about 2 1/2 hours or until cake is puffed and top layer is set. Let stand, covered, 30 minutes before serving. Serve with whipped cream, if desired.