Rinse wild rice in a strainer, lifting the rice with your fingers to thoroughly clean, under cold running water about 1 minute; drain. In a small saucepan, combine the wild rice, the 1 cup water, rosemary, and the 1/2 teaspoon salt. Bring to boiling; reduce heat. Cover and simmer for 40 to 45 minutes or until rice is tender. Remove from heat. Stir in dried cherries. Set aside.
To butterfly the roast, make a lengthwise cut down the center, cutting to within 1/2 inch of the opposite side. Spread open. At the center of each half, make a lengthwise cut parallel to the first cut, cutting to within 1/2 inch of the opposite side. Cover the roast with plastic wrap. Working from center (thicker part) to edges, pound with flat side of meat mallet to 1/2- to 3/4-inch thickness. Make sure the meat is a uniform thickness. Remove plastic wrap. Set aside.
In a large skillet, cook sausage and onion until sausage is browned and onion is tender. Drain fat. Stir in the parsley, thyme, and black pepper. If needed drain the cooked rice mixture to remove liquid. Stir cooked rice mixture into sausage mixture.
Spread the filling over the surface of the butterflied roast. Roll loin up from a long side. Tie with kitchen string. (Wrap several strands of string crosswise around the meat and tie securely.) Place on a rack in a shallow roasting pan. Insert meat thermometer. Roast in a 325 degree F oven for 1-3/4 to 2-1/4 hours or until thermometer registers 155 degree F. Remove from oven. Cover loosely with foil; let stand 15 minutes before carving. (The meat's temperature will rise 5 degree F during standing.)
Remove the pork roast from roasting pan; cover to keep warm. Add 1 cup water to pan, scraping up browned bits. In a small saucepan, use a wire whisk to combine the 1/3 cup cold water and flour. Whisk in pan juices. Cook and stir over medium heat until thickened and bubbly. Cook and stir for 1 minute more. Season to taste with salt and black pepper.
Remove string from pork roast; discard. Slice roast into 8 to 10 slices. Arrange the meat slices on a serving platter. Pour some pan gravy atop meat.