Van der Merwe also scored against both Kenya and Germany in the qualification tournamentCanada secured the final place at next year’s Rugby World Cup in Japan after beating Hong Kong 27-10 in their repechage tournament.
It means the Canucks have now reached their ninth consecutive World Cup.
Hong Kong needed a bonus-point win and to deny their opponents anything from the game if they were to advance.
Canada will now go into Pool B for the tournament alongside defending champions New Zealand, two-time winners South Africa, Italy and Namibia.
Glasgow Warriors winger DTH van der Merwe scored two tries for the Canucks while veteran hooker Ray Barkwill, who will turn 39 a month before next year’s tournament begins, also crossed.
Gordon McRorie added three conversions and two penalties for the side coached by ex-Dragons boss Kingsley Jones.
If Barkwill is selected for Japan, he will be in line to become the second oldest player in the tournament’s history behind Uruguayan legend Diego Ormaechea.