Preheat Oven to 350 - spray 13x9 baking dish - set aside. Brown sausage with onion , drain well, pat dry on paper towels to remove all grease.
In medium pan - heat tomato sauce, tomato paste (both cans), adding 2 cans of water (paste can size) - add italian seasoning...heat til' bubbly - Add 1/2 of sausage - set aside.
Mix together (in another bowl) Ricotto Cheese, Parmesean cheese, beaten egg, and garlic powder, with 1/2 cup Italian blend cheese. Stuff Manicotti noodles (uncooked) with this mixture...easier to stuff when they are uncooked!
In baking pan, put 1 c. Meat/Sauce mixture. Place manicotti noodles in pan....Completely cover with remaining Meat/Sauce mixture, and top with remaining Italian Sausage. Cover with Italian Blend Cheese - Bake coverd 45 min. Uncover and bake til' bubbly and lightly browned.