Preheat oven to 400°F (200°C). Melt 1 tbsp (15 mL) butter in large skillet on medium-high heat. Sauté mushrooms, leek, garlic, rosemary and 1/4 tsp (1 mL) each salt and pepper 6 to 8 min. until mushrooms are golden and tender. Cool completely.
Meanwhile, place turkey breast on cutting board. At the thinner side of the breast, cut in horizontally -- but not all the way through -- to open it up like a book. Lay the breast open between 2 sheets of plastic wrap; pound with meat mallet or rolling pin to 1/2-in. (1-cm) thickness.
Spread mushroom filling evenly over turkey, leaving a 1-in. (2.5-cm) border. Arrange slices of Brie on top of filling. Tightly roll turkey into a log – with he grain running along its length -- tucking in the edges as you roll to enclose the filling. Secure with butcher’s twine. Coat with remaining butter. Season with remaining salt and pepper.
Place turkey roll in small roasting pan fitted with rack. Roast turkey 45 to 50 min. or until the internal temperature reaches 165°F (74°C). Remove turkey from pan. Tent with foil and let rest 15 min.
Meanwhile, combine cherries, red wine, honey and shallot in medium saucepan set over medium-high heat; bring to a boil. Reduce heat and simmer 25 to 30 min. until thick and syrupy. Stir in mustard; cool. Slice turkey and serve with cherry sauce.
Substitute cherries with pitted plums or blackberries.
Call ahead to your local store to order boneless, skinless turkey breast.