Some of the armoured combat vehicles Canada is selling to Saudi Arabia in a controversial $15-billion arms deal will feature medium- or high-calibre weapons supplied by a European subcontractor – such as a powerful cannon designed to shoot anti-tank missiles.

These details shine a light on how lethal a product the Saudi Arabian National Guard – a force that deals with internal threats in the Mideast country – will be getting from Canada.

This contradicts Justin Trudeau's assertion during the federal election campaign that the deal brokered by the Canadian government was merely for what amount to "jeeps."

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It also puts more pressure on Mr. Trudeau's Liberal government to explain why it is allowing the transaction to proceed – particularly after mass executions in Saudi Arabia on Jan. 2 that included a prominent Shia Muslim cleric.

Details about the turreted weapons have been slow to emerge because both General Dynamics Land Systems (Canada) and its Belgian supplier CMI Defence, part of CMI Groupe, are saying little about the contract and subcontract.

Some information has leaked out in Belgium, where one broadcast journalist called CMI's work for the Canadian maker of armoured vehicles the "contract of the century" for the firm, which is based in Seraing, Belgium. Local media say it would be worth €3.2-billion ($4.9-billion) and last more than 15 years. In 2015, CMI announced it had bought a military base in northeastern France to be transformed into a campus to train the Saudis on the LAV weaponry.

The full number of combat vehicles Canada will sell to the Saudis has never been released – some arms trade experts estimate it could be in the thousands – but a French municipal official told The Globe and Mail on Wednesday the transaction CMI is involved with concerns about 700.

CMI, which manufactures turrets and cannons, announced in 2014 that it had signed a large contract with a "Canadian vehicle manufacturer" to supply two gun systems, including a medium-calibre weapon and the Cockerill CT-CV 105HP, which it advertises as a "high-pressure gun with an advanced autoloader to deliver high lethality at very light weight," one with the capacity to fire 105-mm shells and a heavy-armour-penetrating missile. CMI did not name the Canadian company.

In France, where CMI's campus is located, a local municipal official said CMI is doing work for General Dynamics and its armoured vehicle contract with Saudi Arabia. In an interview, Jean-Philippe Vautrin, president of the Communauté de Communes du pays de Commercy, said CMI will start training the Saudis on the turrets and cannons in 2017, using simulators on the campus site but also a nearby artillery range.

He said the Saudis will learn how to operate the wheeled portion of the LAVs on Canadian soil.

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The former Harper government used diplomatic resources to lobby Riyadh for the $15-billion contract, which will support 3,000 jobs in Canada, mainly in London, Ont. A federal crown corporation brokered the deal and is the prime contractor to supply the Saudis with these LAVs.

Foreign Minister Stéphane Dion has rejected calls to cancel or block the deal, saying Canada's reputation would be hurt if it backed out.

His office on Wednesday refused to offer details on what kind of weaponry will be on the Canadian-made LAVs. It referred calls to General Dynamics. A spokesman for the company declined to confirm CMI Defence's involvement, saying General Dynamics "will not respond to speculative inquiries related to our supply chain."

Ken Epps of Project Ploughshares, an anti-war group that tracks arms sales, said the LAV weaponry shows how lethal this Canadian deal is.

"Such vehicles, far from simple troop carriers, are capable of major destruction, and given the ongoing deplorable human rights situation in Saudi Arabia, there is great risk that they will be used against civilians opposed to the Saudi government. This is why the new Canadian government should be reconsidering the Saudi contract," Mr. Epps said.

During the 2015 election campaign, Mr. Trudeau played down the strategic nature of the sale, saying General Dynamics was merely exporting jeeps. Mr. Trudeau went on to characterize the sale as a private contract involving a manufacturing company – omitting Ottawa's crucial role.

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The gun subcontract is at the heart of growing controversy in Belgium, where critics are questioning the wisdom of selling weapons to Saudi Arabia and citing the CMI-General Dynamics deal.

Philippe Hensmans, director of Amnesty International's French-speaking section in Belgium, said the armoured vehicles could be used against civilians or to attack other countries.

"The repression of Shiite groups in the country could potentially be undertaken with these weapons," Mr. Hensmans said in an interview. "The government argues we should be reassured by the fact that they won't be used in countries like Yemen, but rather by police and law-enforcement authorities, but that is still a problem in our view."

Federal rules oblige the Global Affairs department to conduct a special audit of requests to export military goods to countries "whose governments have a persistent record of serious violations of the human rights of their citizens." Among other things, Ottawa must obtain assurances "there is no reasonable risk that the goods might be used against the civilian population."

A Belgian journalist who wrote on CMI's subcontract with General Dynamics, and attended a presentation on the turreted weapons at a military show in 2014, said the firm promotes the versatility of its weapons systems.

"They have developed new technology that reduces the recoil on the cannons, which allows them to install a higher calibre weapon on relatively light vehicles, which … can then be airlifted for operations in different theatres," Michel Gretry said in an interview.