Spray 4 to 5-quart slow cooker with cooking spray. Place roast in slow cooker, cutting to fit and overlapping pieces if necessary. Top with cumin, salt, onion, garlic and taco sauce. Cover; cook on Low heat setting 6 to 8 hours or until fork tender. Remove to cutting board. Remove any fat. With 2 forks, shred meat. For easier eating, cut long shreds with kitchen scissors or large knife. Return to slow cooker; stir to coat with sauce.
Heat oven to 350°F. Spray 13×9-inch (3-quart) glass baking dish with cooking spray. Pour 1/4 cup of the enchilada sauce in bottom of dish. With slotted spoon, divide meat mixture among tortillas, about 1/2 cup each. Roll up and place in dish. Pour remaining enchilada sauce over the top. Sprinkle with cheeses. Bake 25 to 30 minutes or until thoroughly heated, tortillas are golden brown and cheese is melted.
Meanwhile, in heavy (preferably cast iron) skillet, cook corn over medium-high heat 3 to 4 minutes or until lightly browned, stirring once or twice. Remove to medium bowl. Stir in black beans, cilantro, onion, lime juice, salt and pepper.
Serve enchiladas topped with black bean salsa on the side.