Suncor Energy could reap over $8 billion and boost returns to unhappy shareholders if it sells its Petro-Canada gas station business, but Canadian antitrust rules and the need for the unit’s steady profits could deter that move, analysts and shareholders said.Suncor’s poor safety record and lackluster stock performance prompted a demand for changes from activist Elliott Investment Management, so Canada’s second-biggest oil producer replaced its CEO in June and agreed to review its retail fuel unit by the end of this year.