Van der Merwe made the announcement via Twitter earlier, saying: "Having had some time to reflect on this past Rugby World Cup and the past 13 years I've been lucky enough to be a custodian of that Red Maple Leaf Jersey, I've realised that nobody has the divine right to have a fairy tale ending.
"I step away with many fond memories on and off the field. Travelling the world, meeting new people, embracing different cultures are just some of the many blessings of playing this beautiful game.
"I've now lived and enjoyed my Canada 15s dream. I believe it's time to sign off and let someone else fill that jersey and live their dream."