Heat oven to 400°F. Spray 15x10x1-inch pan with cooking spray. In pan, spread corn in single layer. Spray corn generously with cooking spray. Bake about 20 minutes, stirring after 10 minutes, until lightly browned.
Spray 3 1/2- to 4-quart slow cooker with cooking spray. In cooker, mix roasted corn and remaining ingredients except sour cream.
Cover; cook on Low heat setting 7 to 9 hours. Top each serving with dollop of sour cream.