A 63-year-old man with exertional chest tightness is diagnosed with stable angina after normal troponins and a positive exercise stress test. Coronary angiography demonstrates a 70% proximal left anterior descending artery lesion with preserved left ventricular function. His blood pressure is well controlled on an ACE inhibitor and he is already on aspirin and a statin. According to Canadian guidance on stable ischaemic heart disease, which pharmacologic agent is recommended as first-line therapy for symptomatic relief of angina?