Heat 3 tbsp (45 mL) oil in a large Dutch oven over medium-high heat. Season veal shanks with salt and pepper. Dredge shanks in flour, shaking off excess. Working in batches, sear shanks until well browned on both sides, adding oil if necessary. Remove shanks from pan. In same pan, sauté onion, celery and carrot until tender and slightly caramelized, about 5 min. Lightly season with salt and pepper. Stir in tomato paste and cook 2 to 3 min. Add wine to pan, stirring up any browned bits on bottom and cook until reduced by half. Stir in broth, garlic, parsley, rosemary, thyme and bay leaves.
Return shanks to pan and bring to a boil. Reduce heat to a gentle simmer, cover and cook on stove or in a 325°F (160°C) oven until meat is tender, but not falling off the bone and sauce has thickened, about 60 min. covered, then 30 min. uncovered.
Transfer shanks to a serving platter. Strain cooking liquid and measure out 2 cups (500 mL). Mix with marinara sauce, season to taste and spoon over veal shanks.