Preheat oven to 400 degrees Fahrenheit.
Remove innards from chicken and rinse with cold water. Let drain in a large colander for 2 minutes.
Pat chicken dry and place in roasting pan, breast side down. Pour champagne/sparkling wine all over and inside the chicken. Do the same with the orange and lemon juice. Season with salt and pepper.
Place the juiced orange and lemon halves, their unjuiced other halves, plus the additional lemon, and stuff inside the chicken. Prick the whole lemon a few times with a fork before stuffing it to help release the juices inside the chicken.
Place chicken in oven and turn down heat to 350 degrees Fahrenheit. Roast, uncovered, for 15 minutes.
Remove chicken from oven and, using tongs or wooden spoons, flip chicken over so that the breast side is now facing up.
Return to oven and continue cooking until a meat thermometer inserted into the thigh reads 180 degrees Fahrenheit. Start checking the temperature after about an hour and a half. For the last 10-15 minutes of cooking, add shallots and grapes to bottom of roasting pan.
Once meat thermometer reads 180 degrees Fahrenheit, remove from oven. Transfer grapes and shallots to a serving platter first, and then transfer chicken so it sits in the middle of the grapes and shallots. Garnish with fresh sage and thyme sprigs. Use a carving fork and knife to serve.