Marion Thees took silver.
Yarnold travelled to Canada and the Olympic track from 2010 having taken silver last time out in Park City to jump up to fourth in the overall World Cup standings.
However a second consecutive medal looked far off after the first run in Whistler with the 24-year-old ranked seventh after clocking a time of 55.70seconds.
She was much better second time though at the track where Amy Williams won Olympic gold, and posted 55.47 to lead until there were only three sliders left.
Reid recovered from a poor start and entrance into corner one to beat Yarnold’s overall time by 0.08 however Cassie Hawrysh couldn’t follow suit.
That secured Yarnold at least a bronze medal and that was what she collected as Thees, leader after run one, comfortably took victory after run two.
Thees, who posted 55.39 in run one, clocked 55.53 second time out to take victory by 0.17 ahead of Canadian Reid and become the third different winner this season.
She now leads the World Cup standings with 609 points with Katie Uhlaender, who was seventh, second with 577, Reid third with 571 and Yarnold fourth with 562.
Bronze does represent Yarnold’s fourth World Cup medal in less than a year competing on the circuit and she was once again comfortably the best Brit.
Olympic silver medallist from 2006 and reigning World Cup champion Shelley Rudman improved from 11th after run one to finish ninth after the second.
However that was her worst finish of the season so far and yet another off the podium while the third Brit in action Donna Creighton went from 18th to 17th.
And making Yarnold’s result and comeback all the more impressive was that her training time in Whistler was severely interrupted by an accident in practice.
“I had quite a tough training week, I suffered a really bad blackout on the second day and that meant I only had half the amount of training runs,” said Yarnold.
“So to come out and get on the podium again, I am over the moon, I am so overwhelmed.”