A 71-year-old man with moderate chronic obstructive pulmonary disease (COPD) reports persistent exertional dyspnoea despite good adherence to a long-acting muscarinic antagonist (LAMA). He has had two moderate exacerbations in the past year requiring oral steroids but no hospital admissions. According to the 2023 Canadian Thoracic Society COPD pharmacotherapy guideline, what is the most appropriate next step?