A 65-year-old man presents with worsening shortness of breath and pleuritic chest pain. He recently had a hip replacement and has been relatively immobile. Oxygen saturation is 90% on room air, heart rate 110 beats/min, blood pressure 126/76 mm Hg. D-dimer is markedly elevated. CT pulmonary angiography confirms a segmental pulmonary embolism. According to Canadian VTE guidelines, what is the recommended initial anticoagulant in most stable patients without cancer or severe renal disease?