Philip Snyman, Cecil Afrika, Seabelo Senatla and Kwagga Smith scored for the Blitzboks, who moved past Fiji into first place in the overall standings.
Sean Duke, Mike Fuailefau, Lucas Hammond and Pat Kay scored tries as Canada won the consolation Bowl competition, defeating Kenya 24-5 to finish ninth.
The Canadians moved up one spot in the overall standings to 12th spot after three events. The top four finishers after all nine stops qualify automatically for the 2016 Olympics.
After going 1-2 on the opening day, Canada opened Sunday with a 22-5 win over Zimbabwe, Canadian coach Liam Middleton's former team. Duke scored two tries.
Canada then beat Wales 24-14, rallying from 14-7 down at the break on tries by Conor Trainor, Sean Duke and Ciaran Hearn, before defeating Kenya.