Trim excess skin and fat from duck and reserve for other use. Place duck on rack in roasting pan; set aside.
In a small saucepan, heat oil over medium heat and cook shallots and garlic for about 6 minutes until softened.
Add port and bring to a boil. Reduce heat and simmer for about 15 minutes or until reduced by half.
Using a small paring knife, pierce skin a few times; sprinkle duck with salt, inside cavity and on skin. Place sage leaves and shallots into duck cavity. Remove about 1/2 cup of port mixture and brush all over duck. Add cherries to remaining port and set aside.
Place duck in centre of a 325°F oven and roast for about 3 hours until skin is crisp and golden brown
Let stand for 10 minutes before cutting.
Reheat port and cherries and serve with duck