The Barbarians are an invitational side featuring players from across the globe and known for its attractive, free-flowing style of play. Tuesday game is part of their 125th anniversary year.
The matchday squad against the Tigers includes players from Australia, Canada, England, Ireland, New Zealand, Samoa, Scotland and South Africa.
Duke, a 26-year-old winger from Vancouver, and Marshall, a 29-year-old prop from North Vancouver, will start on the Barbarians bench at Welford Road.
They will rejoin the Canada camp in time for Friday's test match against Namibia in Wales.
The two players were on the Canadian team bus Monday morning when they were called to the front. Marshall thought they might be in trouble, wondering whether they had forgotten to pay some personal costs on their hotel bill. Instead they were told they would play for the Barbarians.
A dream come true?
"Not necessarily a dream because I never really thought that it could possibly happen," an over-the-moon Marshall said in an interview.
Since 1890, players from more than 25 different countries have worn the famous black-and-white hooped jersey (players wear their domestic club socks when they play for the Baa Baas). Once invited, a player becomes a life member of the famous club.
Marshall, a former Simon Fraser University quarterback, will wear red Canadian team socks. He didn't have his club ones with him.
Leicester, one of England's powerhouse teams, won its record 10th Premiership title in 2013. Once home to Canadian star winger Winston Stanley, the injury-plagued Tigers currently stand eighth in the Aviva Premiership with a 3-3-0 record.
Leicester lost 52-42 to the Barbarians when the two sides met in 2006. The Tigers do hold wins over the New Zealand Maori and South Africa.
Duke and Marshall, as well as Worcester Warriors hooker Neil Annett, were summoned after fly half Colin Slade and hooker James Parsons were called into the New Zealand squad for the remainder of its November tour series. Australian back Tom English was also called in.
"We're very grateful to the head coaches of Australia, Canada and Worcester for releasing these players to join us," Barbarians head coach John Kirwan, a former All Blacks star back, told the Tigers website. "It's a great gesture on the part of Michael Cheika, Kieran Crowley and Dean Ryan, and we hope all four players enjoy their time with us."
Slade and Parson both played in the Barbarians' 40-36 loss to Australia on Saturday before nearly 50,000 fans at Twickenham.
"This is a great opportunity for Sean and Jason to play alongside some of the world's best players and join the world's most famous club," Rees, Canada's men's program manager, said in a Rugby Canada statement.
"These types of opportunities for Canadian players are increasingly rare since the onset of professional rugby. I am delighted for them both and that they will both don the famous jersey," he added.
Rees and Crowley, a former All Black who now coaches Canada, both have ties to Kirwan.
Charron played five times for the Barbarians from 1994 to 2000 while Rees saw action in three games in 1993 and '94. Other Canadian Barbarians include Glen Ennis (1992), Kevin Tkachuk (2006), David Lougheed (1995), Rod Snow (1996 and 2004) and Wyatt (1991).
In the early 1960s, the Barbarians asked Douglas (Buzz) Moore to play against Canada while on tour in Britain. He declined, leading the Canadians to a 3-3 tie against the all-stars. The Barbarians made him an "honorary Barbarian."
Duke is a veteran of the Canadian sevens team, playing at the Commonwealth Games in Glasgow this summer and recent first leg of the IRB Sevens World Series in Australia. He played 80 minutes on the wing Sunday in a 28-23 Canada loss to Championship XV, an all-star side from English rugby's second tier.
"To be selected to play for the Barbarians is a huge honour for me and I am looking forward to experiencing their unique brand of rugby before returning to focus on Namibia," Duke said.
The Barbarians are fresh off a 40-36 loss to the Australian Wallabies on Saturday at Twickenham in front of nearly 50,000 fans at the home of the RFU in London.
Marshall, who did not play Sunday against the Championship XV, recently made it to the final of the ITM Cup Championship in New Zealand with Hawke's Bay. He lost to a Manawatu Turbos side featuring fellow Canadian prop Hubert Buydens, who is captaining Canada on tour.
He took a gamble on going to New Zealand after a less than enjoyable season in France. He ended up playing every game for Hawke's Bay.
"Pretty awesome so far," he said of his recent rugby journey.
The Canadian team left Leicester on Monday for north Wales to prepare for the test against No. 22 Namibia in Colwyn Bay.
Canada, ranked 17th in the world, heads to France after that to face No. 9 Samoa in Vannes on Nov. 14, and No. 16 Romania in Bucharest on Nov. 22.
Samoa, Namibia and Romania will join Canada at next year's World Cup, with Canada and Romania both featured in Pool D, alongside No. 5 Ireland, No. 7 France, and No. 14 Italy.
Tevita Li (Blues), Frank Halai (Blues & New Zealand), Juan de Jongh (Stormers & South Africa), Francis Saili (Blues & New Zealand), Nick Cummins (Coca Cola West Red Sparks & Australia), Marnitz Boshoff (Golden Lions & South Africa), Fumiaki Tanaka (Highlanders & Japan), Lourens Adriaanse (Sharks), Mahonri Schwalger (Chiefs & Samoa), Thomas Du Toit (Sharks), Dominic Bird (Canterbury & New Zealand), Al Kellock (capt., Glasgow & Scotland), Michael Rhodes (Stormers), Heinrich Brussow (Cheetahs & South Africa), Jacques Botes (Sharks).
Niall Annett (Worcester Warriors), Jason Marshall (Hawke's Bay & Canada), Matt Stevens (Sharks & England), Angus Ta'avao (Blues), Steven Luatua (Blues & New Zealand), Matt Todd (Crusaders & New Zealand), Adam Thomson (Canon Eagles & New Zealand), Sarel Pretorius (Cheetahs), Sean Duke (UVIC & Canada), Tom English (Rebels).
Freddie Burns, Miles Benjamin, Christian Loamanu, Anthony Allen, Vereniki Goneva, Owen Williams, David Mele, Michele Rizzo, Jake Farnworth, Fraser Balmain, Harry Wells, Sebastian De Chaves, Laurence Pearce, Jamie Gibson, Jordan Crane (capt.).
George Nairn, Tom Bristow, Tiziano Pasquali, Charlie Beckett, Paul Grant, George Tresidder, Tommy Bell, Adam Thompstone.
Follow @NeilMDavidson on Twitter