Coat roast with marinade; place in a resealable plastic bag. Add cola, squeeze out air and seal bag. Refrigerate overnight, turning once or twice.
Preheat barbecue to medium and lightly oil grill. Combine sauce, broth, rosemary, thyme, garlic and pepper in a medium-size aluminum roasting pan. Remove roast from marinade; pat dry and discard marinade.
Sear roast on all sides. Place roast on upper rack and roasting pan directly below roast on grill. Place a meat thermometer in centre of roast, reduce heat to low and close lid. Cook until roast reaches 160°F (71°C) for medium, about 3 hours, basting every 20 min. with sauce.
Remove roast to cutting board, loosely cover with foil and let rest 30 min. Shave or slice very thinly and serve on Kaiser rolls with some of the sauce.