A 45-year-old man presents with 3 months of exertional central chest tightness radiating to his left arm, relieved by rest within 5 minutes. The pain is consistently triggered by climbing two flights of stairs and has not changed in pattern. He is a non-smoker with borderline hypertension. Physical examination and resting ECG are normal. According to Canadian stable ischaemic heart disease guidance, what is the most appropriate next diagnostic step?