I think this is in reference to the Papal Zouaves, a 'foreign legion' in the service of the Holy See during the papacy of Pius IX. I've read cursorily about them, but hadn't heard of the Canadian angle — I've just done some more reading, and it does seem that several hundred French Canadians joined up.

Here's something, from Jean Guenel's La derniere guerre du pape — translation sourced from an essay by John C. Rao:

> "Finally, one must speak of the one hundred thirty Canadians from Quebec, who will arrive in 1868. They will not have the chance to fight, but some will participate nonetheless in the siege of Rome. Another wave of one hundred twelve volunteers left Canada in August of 1870 to engage."

Source, per Rao: Jean Guenel, La derniere guerre du pape (1998), p. 40)

That seems to tally with this excerpt on the Canadian Zouaves, from Charles C. Colcombe's The Pope's Legion:

> In Canada, the news of [the Battle of] Mentana rocked the country — particularly the province of Quebec. In every French-Canadian parish (and many English-speaking ones), a recruiting drive was launched in the manner of a new crusade. [...] > > Having survived as a culture for over a century after the English Conquest, French Canada was undergoing an interior change — its people were beginning to see themselves as a nation and as a bastion of French and Catholic culture in a continent overwhelmed by Anglo-Saxon Protestantism. One of the leading lights of this current was Mgr. Ignace Bourget, the fiery bishop of Montreal. Foremost among the cheerleaders for the new crusade, on February 18, 1868, he hosted a ceremony for the new recruit at Montreal's Notre Dame cathedral. A milestone in the history of the French Canadians, it featured the presentation of a regimental banner to the first party of 137 recruits to depart for Italy. > > [...] > > Six more detachments set off for the Eternal City between February of 1868 and September of 1870, for a total of 507 men. Among these men were several who would play key roles in the formation of French Canada's identity — such as Ephrem Brisebois, later to find fame as an officer of the Canadian Mounted Police, Ernest Lavigne, the noted musician, and Joseph Couture, who would pioneer Canada's quarantine system.

Source: Charles C. Colcombe, The Pope's Legion: The Multinational Fighting Force That Defended the Vatican (2009), pp. 146-147.

Edit: typo.