Van Koeverden raced to silver in men's kayaking while Oldershaw followed about 15 minutes later with a bronze in canoeing.
Later in the day, Huynh captured bronze in women's wrestling.
The medals boosted Canada's total at the London Games to 14 — one gold, four silver, nine bronze, just four shy of what the country managed in Beijing.
Winning medals on the same day at the same venue was special for van Koeverden and Oldershaw. The pair have trained together out of the Burloak Canoe Club in Oakville, Ont., since they were teenagers.
"Oh man, I'm happy for him," van Koeverden said of Oldershaw.
For van Koeverden, it was his fourth Olympic medal. He won gold and bronze at the Athens Games in 2004 and a silver in Beijing four years ago.
After setting the pace with a blazing start in the men's K-1 1,000-metre final, van Koeverden lost gold to friend and longtime training partner Eirik Veras Larsen of Norway in the final stretch.
"I started the way I wanted to," said van Koeverden, an Oakville native. "I was super-comfortable. Going through the 500 I had tons of energy. It's not a case of a screwed-up race plan, this is a case of one guy in the whole world being better than me. And I can live with that.
"Seven billion people, one guy's better. It's OK."
Oldershaw, who comes from a family of Olympic paddlers, was a full second out of fourth place with 250 metres remaining in the C-1 1,000 but powered his way onto the podium.
What made it extra special for the third-generation Olympian was that almost his entire family was at Dorney Lake to share his joy.
"My mom, my dad, my sister, my girlfriend, cousins, uncles, aunts. Everyone is here," the Burlington, Ont., native said, before breaking off to give his mother, Connie, a big hug.
"I'm so happy to be a Canadian and to be an Oldershaw. To represent both is a great feeling."
Huynh made it a three-medal day for Canada when she beat Isabelle Sambou of Senegal to finish third in the 48-kilogram category.
Huynh, who grew up in Hazelton, B.C., but now lives in Calgary, won gold at the 2008 Games but missed out on a chance to defend her crown when she lost to Japan's Hitomi Obara in the semifinals.
"It's fantastic. I'd prefer it was gold, but I'll take bronze. I'm just so happy to be here and represent Canada," Huynh said. "I would love to be on top of the podium again. What an amazing feeling that was four years ago, but I'm still pretty happy."
Martine Dugrenier of Laval, Que., had a chance to add a second wrestling podium finish, but she lost to Battsetseg Soronzonbold in the bronze-medal bout of the 63-kilogram division.
Elsewhere, Damian Warner of London, Ont., sits third halfway through the men's decathlon. The final five events go Thursday.
"I feel great. I made it a goal to just come out and have fun and I knew the score would just come," Warner said. "My hurdles are strong, 1500 metres is strong, discus is getting better and I'm consistent in the pole vault.
"The score and placing after Day 1 doesn't surprise me, I have very high expectations of myself."
It was a good morning on the track as Cam Levins of Black Creek, B.C., advanced to the semifinals in the men's 5,000-metres, while Jessica Smith of North Vancouver, B.C., moved on in the women's 800.
Levins built off his impressive 11th-place finish in the 10,000 metres earlier in the Games and set a personal-best time of 13 minutes 18.29 seconds to advance out of the heats.
"I'm glad to have made it through," said Levins. "I was more confident in the 5K than the 10K. I knew I just needed to get to the last lap and go."
Smith advanced by finishing second in her heat. It was a slow group and came down to a sprint for the finish.
"I just stuck in there," she said.
The Canadian women's soccer team received some good news as it went through final preparations for Thursday's bronze-medal game with France.
FIFA announced that a probe into the behaviour of players following a heartbreaking semifinal loss to the U.S. wouldn't be completed until after the Olympic tournament.
A number of Canadian players, including inspirational captain Christine Sinclair, criticized the Norwegian referee and could have been banned for the third-place match.
"Good news this morning," Canada coach John Herdman said. "We were on tenter hooks, in danger of losing a key player, but more, just the danger of the game losing an opportunity of seeing such a great player playing in a bronze-medal match."
Montreal's Meaghan Benfeito and Roseline Filion of Laval, Que., who combined to win bronze in women's 10-metre platform synchronized diving, both qualified for the semifinal of the individual event.
In individual show jumping, 10-time Olympian Ian Millar of Perth, Ont., finished tied for ninth, while defending gold medallist Eric Lamaze of Schomberg, Ont., failed to make the final round.
"I think my mare is tired. She has jumped a lot of big courses here and she hasn't a lot of experience," Lamaze said. "I did not wake up this morning imagining myself on the podium so I am not too sad."
In other Canadian results:
— In track and field, Jared Connaughton of New Haven, P.E.I., and Toronto's Aaron Brown failed to advance to the final of the men's 200 metres.
— Hilary Stellingwerff of Grand Bend, Ont., and Winnipeg's Nicole Sifuentes failed to advance of the semifinals of the women's 1,500 metres.
— Tory Nyhaug of Coquitlam, B.C., finished 20th in the men's seeding event in BMX cycling with a time of 39.515 seconds.
— Curtis Moss of Burnaby, B.C., finished 22nd in qualifying for the men's javelin throw and did not advance to the final.