Combine all of the ingredients except crab and shrimp in a large saucepan and cook over medium-low heat, stirring until cheeses are thoroughly melted and mixture is smooth. Stir in crab and shrimp; cook for another few minutes. Pour mixture into an 8-inch baking pan or souffle pan.
Bake for 25-30 minutes, until top is golden brown.
Serve hot with sliced French baguette or crackers. Keep warm with a chafing dish.