In a small bowl, stir together the garlic, parsley, celery leaves, salt, and corn oil; set aside. Bring a large pot of lightly salted water to a boil over high heat. Pour in the peas, and return to a boil. Stir in the scallops, and boil for 3 minutes, then add the shrimp and continue cooking for 1 1/2 minutes more. Drain well, then cool in the refrigerator for 30 minutes.
Once the seafood has cooled, toss it with the garlic dressing until coated. Refrigerate overnight before serving.