Preheat oven to 400°F.
Score the loaf of bread parallel and perpendicularly to form one-inch cubes; make sure not to cut through the base of the loaf.
Arrange loaf on a baking sheet and carefully loosen the cubes to form small crevices between them. In a large mixing bowl, combine the corned beef, sauerkraut and shredded Swiss then stuff mixture in-between the bread cubes, making sure to distribute everything evenly. Transfer to oven and bake until cheese is bubbly, about 10- 12 minutes.
Meanwhile, in a mixing bowl, combine sour cream, ketchup and relish. Season with salt and pepper then pour into a squeeze bottle.
Remove bread from oven and top with the ketchup and sour cream sauce.