Preheat the oven to 425 degrees. Mist 2 large baking sheets with cooking spray. In a small baking dish, mix together 2 tablespoons lime juice with garlic, chili powder, cumin, and 1 teaspoon olive oil. Add salmon and turn to coat; let sit.
In a medium bowl, toss corn, bell pepper, poblano pepper, and onion with remaining 2 teaspoons olive oil. Transfer corn mixture to one of the baking sheets; spread into a single layer.
Remove salmon from marinade and arrange on second baking sheet. Drizzle corn mixture with remaining salmon marinade. Season salmon and corn with salt and black pepper to taste and roast 8 to 10 minutes, until fish is just cooked through and vegetables are tender.
Mix together sour cream, cilantro, and remaining lime juice. Season with salt to taste. Spoon corn onto plates and add salmon. Drizzle cream over fish.