Sprinkle the chicken liberally with salt and pepper. Heat the canola oil in a large, ovenproof high-sided skillet over medium-high heat until it shimmers. Sear the chicken, skin-side down, until golden brown, 3 to 4 minutes. Then flip and brown the other side, 3 to 4 minutes. You may need to do this in two batches to avoid crowding the skillet. Transfer the browned chicken and any juices to a baking sheet or large plate.
Lower the heat to medium and add the garlic, 1 cup of the grapes, the olives, capers, oregano, wine and 1/2 cup water. Stir to combine and cook until the liquid has reduced by half, 6 to 8 minutes. Stir in the butter. Add the chicken and any juices back to the skillet, skin-side-up. Sprinkle the remaining grapes around the chicken. Continue cooking over medium heat until the internal temperature reaches 75°C, 6 to 8 minutes.
Set the oven to broil with a rack set about 4 inches from the broiler.
Place the skillet underneath the broiler to crisp the chicken skin, about 2 minutes. Watch carefully to avoid burning.
To serve, divide the warm couscous among 4 plates and top each plate with 2 of the chicken thighs and a large spoonful of the sauce.