Heat over to 425 degrees. Coat a baking sheet with cooking spray. Toss potatoes and onion with canola oil in a bowl; season with salt and pepper; spread evenly on baking sheet. Bake until crispy yet fork-tender, 20 to 25 min. Cool to room temp. Return to bowl; add corn, celery and garlic powder. Whisk olive oil and vinegar in a bowl; drizzle over potatoes and onions; toss to coat well. Season with salt and pepper. Cover, frig. at least 2 hrs.. and up to 8 hrs. Stir in basil before serving.
Cooking corn: Soak unhusked ears of corn in water for 10 to 15 min. Heat oven to 375 degrees. Cook ears in a shallow pan until kernels are tender, about 25 min. Let cool. Remove and discard husks and silk; slice kernels off cob. Three ears of corn should yield about 1 1/2 c. of kernels.
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