A 71-year-old man with a 50 pack-year smoking history and longstanding chronic obstructive pulmonary disease (COPD) reports increasing dyspnoea on exertion. He remains breathless walking one block on the flat. He has had two moderate exacerbations requiring prednisone and antibiotics in the last year. Current medications include a long-acting muscarinic antagonist (LAMA) alone. Oxygen saturation is 95 percent on room air. According to Canadian COPD guidelines, what is the most appropriate adjustment to his inhaled therapy?