If using whole tomatoes, in blender or food processor, puree tomatoes with juice. Set aside. In large, heavy pot over moderate heat, heat oil until hot but not smoking. Add pancetta and saute until golden brown, 5 to 6 minutes. Add beef, pork, and veal and saute, breaking up meat with back of spoon, until browned, 7 to 8 minutes. Add onion and carrot and saute until vegetables are tender, 5 to 6 minutes. Stir in red wine and simmer, scraping up browned bits stuck to bottom of pan, until liquid is reduced by half, about 5 minutes. Stir in tomatoes, cream, salt, and pepper. Reduce heat to moderately low and simmer, uncovered, stirring occasionally, until sauce is thickened and brick-red in color, approximately 30 minutes. In large pot of boiling salted water, cook pasta until almost tender. Drain well and toss with sauce. Serve with grated cheese.