Add in the mushrooms, onions, and garlic; stir/sauté for 5 minutes or until tender.
Stir in flour; blend well.
Add in stock, cream, wine, and seasonings; stir about 2 minutes or until thickened.
Stir in cheese, shrimp, and crabmeat.
In a 4-quart casserole dish lightly coated with cooking spray combine spaghetti and seafood sauce (you can combine the spaghetti and seafood in a bowl, then transfer to the prepared casserole dish, if preferred).
Sprinkle with Parmesan cheese.
Bake, uncovered, for about 45 minutes or until bubbly.