In a large bowl, toss together the flour, masa harina, bread crumbs, baking powder, sugar, salt, and pepper; set aside. In a separate bowl whisk together the milk, canola oil, and eggs, blending well. Fold the milk mixture into the dry mixture, mixing thoroughly. Stir in the corn, bell peppers, jalapenos, cilantro, and shallots, blending well. Gently stir in the crabmeat and shrimp, taking care not to break up the lumps of crabmeat.