A 40-year-old man presents to the emergency department with sudden-onset pleuritic chest pain and dyspnoea. He has no leg swelling, heart rate is 96 beats/min, oxygen saturation 97% on room air, and no recent surgery or cancer. His Wells score for pulmonary embolism is calculated as 2 (moderate pre-test probability). According to Canadian-adapted diagnostic strategies, what is the most appropriate next step?