A 64-year-old woman with a 40-pack-year smoking history and chronic cough presents with exertional dyspnoea and wheeze. Spirometry after appropriate bronchodilator testing shows FEV1/FVC ratio 0.60 and FEV1 65% predicted, with minimal reversibility. She has one moderate exacerbation per year treated with oral corticosteroids. According to Canadian Thoracic Society guidance, which is the most appropriate initial maintenance pharmacotherapy?