Preheat oven to 350 degrees. Spray a 13 x 9 in. baking dish with cooking spray.
In a bowl, combine crab, shrimp, mayonnaise, onion, celery, taco seasoning, and 1 cup of cheddar cheese.
Divide the crab mixture evenly among the tortillas. Roll up the tortillas and place them seam-side down into the prepared baking dish.
Pour the enchilada sauce over the tortillas and sprinkle with the remaining 1 cup of cheddar cheese.
Bake the enchiladas, uncovered, for 20 minutes or until hot and bubbling.