Preheat the oven to 375 degrees. Grease a loaf pan.
Mix together the stuffing mix and tuna in a large bowl. Set aside.
In a medium bowl combine the mayonnaise, sour cream, chicken broth, and egg. Mix well to combine.
Add the mayonnaise mixture to the stuffing mixture and mix until combined.
Stir in the onions, garlic, celery, pepper, Dijon, salt, black pepper, and seafood seasoning. Mix well.
Spread into the loaf pan.
Bake for 55-60 minutes or until the top is browned. Remove from oven and cool for 5 minutes. Cut and serve from the pan.