Heat 1/4 cup margarine in a large skillet, and cook and stir the celery, onion, and garlic over medium heat for about 5 minutes, until onion is translucent. Stir in the chopped clams and salad shrimp, and cook and stir about 3 more minutes, until the mixture is hot. Drain most of the liquid from the skillet, leaving about 1 tablespoon.
Sprinkle in the chicken bouillon granules, cayenne pepper, and white pepper, and stir. Gently stir in the croutons, bread crumbs, and crab meat.
Preheat an oven to 400 degrees F (200 degrees C).
Melt 1/4 cup of margarine in the bottom of a 9x13 inch baking dish, and pour in the white wine. Mound about 1/3 cup of filling into each mushroom cap, and place them into the baking dish. Sprinkle the Italian blend cheese over the mushroom caps.
Bake in the preheated oven for about 20 minutes, until the cheese is bubbling and starting to brown.