Having done a little more reading, I find that to be a less-than-accurate description of what happened.
"In 1970, members of the FLQ kidnapped British diplomat James Cross and Quebec provincial cabinet minister Pierre Laporte, who was later murdered. What is now referred to as the October Crisis raised fears in Canada of a militant terrorist faction rising up against the government.
Under provisions of the National Defence Act, the Canadian Forces had been called to assist the police. They appeared on the streets of Ottawa on 12 October 1970. Upon request of the Quebec government with unanimous consent of all party leaders in the Quebec National Assembly, troops appeared on the streets of Montreal on 15 October.[24]
At the request of the Mayor of Montreal, Jean Drapeau, and the Quebec provincial government, and in response to general threats and demands made by the FLQ, the federal government declared a state of apprehended insurrection under the Act on 16 October 1970." This last was an invocation of the War Measures Act, which was already on the books.
At the time, 86% of French-speaking Canadians supported use of the War Measures Act.
So, your "ignoring the rule of law" seems actually to be "using the laws already on the books, with popular support, at the request of the government of Quebec at the time".
Was it ham-handed? Probably. But it seems to have been entirely legal.
https://en.wikipedia.org/wiki/October_Crisis#War_Measures_Act_and_military_involvement
https://en.wikipedia.org/wiki/War_Measures_Act