Trudeau invoked the War Measures Act at the request of the Premier of Quebec, and the Mayor of Montreal.   Simultaneously, the Solicitor-General of Quebec requisitioned the deployment of the military from the Chief of the Defence Staff in accordance with the National Defence Act. Troops from Quebec bases and elsewhere in the country were dispatched, under the direction of Quebec's provincial police force to guard vulnerable points and prominent individuals at risk. This freed the police to deal with the crisis.

Outside Quebec, mainly in the Ottawa area, the federal government deployed troops under its own authority to guard federal offices and employees. The combination of the increased powers of arrest granted by the War Measures Act and the military deployment requisitioned and controlled by the government of Quebec, gave appearance that martial law had been imposed. But, the military remained in a support role to the civil authorities and never had a judicial role.

Once the War Measures Act was in place, arrangements were made for all detainees to see legal counsel. In addition, the Quebec Ombudsman, Louis Marceau, was instructed to hear complaints of detainees and the Quebec government agreed to pay damages to any person unjustly arrested. On 3 Feb 1971, Minister of Justice John Turner reported that 497 persons had been arrested under the War Measures Act, of whom 435 had already been released. The other 62 were charged, of which 32 were crimes of such seriousness that a Quebec Superior Court judge refused them bail.

The October Crisis was the most serious terrorist attack to occur on Canadian soil in the 20th Century.

At the time, opinion polls in Quebec and the rest of Canada showed overwhelming support for this move. Politician and future Parti Québécois Premier René Levesque wrote that he agreed it was necessary under the circumstances.

Source:
http://www.canadiansoldiers.com/history/domesticmissions/flqcrisis.htm