In a large bowl, stir together the marscapone cheese, powdered sugar, pumpkin, ricotta cheese, and pumpkin pie spice until smooth. Stir in 1/4 cup of the toasted nuts. Set aside.
In a chilled mixing bowl, beat cream with an electric mixer until stiff peaks form. Fold into pumpkin mixture. If desired, cover and chill up to 4 hours.
To serve, spoon pumpkin mixture into a self-sealing plastic bag. Snip a 3/4-inch hole in one corner. Pipe filling into cannoli shells so pumpkin filling extends from ends. Sprinkle cannoli ends with remaining nuts.
Arrange on platter and sprinkle with sugar.
NOTE: If purchased cannoli shells are not available, brush one side of 16, 4-inch flour tortillas with cooking oil. Roll, forming a tube shape; secure with wooden toothpick. Gently place a rolled piece of foil in the center for support. Place on baking sheet; brush outside with oil and bake in a 375*F oven for about 15 minutes or until golden brown. Place on wire rack to cool. Remove foil and toothpicks; fill with pumpkin mixture. Makes 16 shells (allows for breakage).