Season rabbit pieces and dust lightly with flour. Heat oil in a large skillet over medium-high heat. Add onion and sauté for 3 to 4 minutes. Add rabbit pieces and brown each evenly.
Add wine, broth, vinegar, sugar, bay leaves, rosemary and salt. Bring to a boil, then reduce heat to low.
Cover and simmer for 1 1/2 hours or until rabbit pieces and tender and can be pulled away from the bone with little pressure.
Add pears to the pan, cover and simmer for 30 minutes more.
Remove rabbit and pears and arrange on plates. Remove bay leaves and rosemary from pan.
Whisk in butter until melted and spoon sauce over rabbit.