Combine buttermilk, 1 tsp garlic powder, ½ tsp paprika, ¼ tsp cayenne pepper, 1 tsp salt, and ½ tsp black pepper in a large bowl or resealable bag.
Add chicken tenderloins, ensuring all pieces are fully submerged. Seal and refrigerate for 4 to 24 hours.
Whisk together flour, cornstarch, 1 tsp garlic powder, 1 tsp onion powder, 1 tsp paprika, ¼ tsp cayenne, 1½ tsp salt, and ¾ tsp black pepper in a shallow dish.
Remove each chicken piece from buttermilk, letting excess drip off. Dredge in the seasoned flour mixture, pressing firmly. Dip back into buttermilk briefly, then coat in flour a second time.
Heat 3 inches of peanut oil in a Dutch oven or heavy-bottomed pot to 350°F.
Fry chicken in batches of 3–4 pieces for 4–5 minutes per side, until deep golden brown and the internal temperature reaches 165°F.
Transfer cooked chicken to a wire rack set over a baking sheet. Season lightly with salt immediately.
For Cane's sauce: Stir together mayonnaise, ketchup, Worcestershire sauce, ¼ tsp garlic powder, ¼ tsp black pepper, and a pinch of salt. Refrigerate for at least 30 minutes before serving.
Serve chicken fingers with Cane's sauce, crinkle-cut fries, Texas toast, and coleslaw.
