Sarah Black of Ottawa, Christine Roper of Victoria, Natalie Mastracci of Thorold, Ont. and Cristy Nurse of Georgetown, Ont., were second in 6:47.62.
The U.S. won gold in 6:43.15 and the Aussies picked up bronze in 6:49.26.
"It felt amazing,” said Mastracci, an Olympic silver medallist in the women's eight at the 2012 Olympics in London.
”After our preliminary race we felt we had some work to do, we did exactly that,”
The silver medallists are also members of the women’s eight and will compete in the final on Sunday.
In the lightweight men's pair final, Eric Woelfl of St. Catharines, Ont., and Brendan Hodge of Delta, B.C., finished just out of the medals in fourth overall.
The Swiss crew won the race in 6:48.85 ahead of Italy (6:51.48) and Great Britain (6:52.08). Canada's time was 6:57.58.
Also Friday, Canada's men's and women's lightweight singles rowed in B finals.
Both Nick Pratt of Kingston, Ont., in the men’s race and Patricia Obee of Victoria were ninth overall.
The men's four was second in its final race to finish 14th overall. The crew members are all Olympians: Will Crothers of Kingston, Ont., Will Dean of Kelowna, B.C., Conlin McCabe of Brockville, Ont. and Rob Gibson of Kingston, Ont.
The Canadian men's pair of Spencer Crowley of Lantzville, B.C., and Steve Van Knotsenburg of Beamsville, Ont., was fifth in the C final and 17th overall.
In addition to the women’s eight final, Canada will also shoot for a medal this weekend in the women's quad.