Combine the first 5 ingredients in a large bowl. Mix on medium speed using a hand mixer until blended. Fold in the crab and shrimp. Transfer to a shallow 2-cup baking dish. Top with Parmesan. Bake for 20 minutes or until top is lightly brown.
To make the toasted bread slices, place bread slices on a baking sheet. Brush with olive oil on both sides. Bake in oven for 8 minutes while dip is also baking. Serve crab and shrimp dip with toasted bread slices.