But if the public response of last October is anything to go by, Canadians will respectfully, resiliently and quickly return to business as usual.
It was just after 9 a.m. on a brilliant autumn Wednesday morning last Oct. 22 when, in the words of many observers, the country "lost its innocence."
Cpl. Nathan Cirillo, 24, was gunned down from behind as he stood ceremonial guard at the National War Memorial adjacent to Parliament Hill. From there, the lone gunman raced up to Canada's seat of government and stormed through the front doors under the Peace Tower before dying in an hail of bullets, including those fired by the sergeant-at-arms of the House of Commons.
The gunman, Michael Zehaf Bibeau, fell only a few steps from where Prime Minister Stephen Harper and official Opposition Leader Tom Mulcair were meeting with their respective national caucuses in rooms on opposite sides of the Hall of Honour.
Coming just 48 hours after Warrant Officer Patrice Vincent, 53, was murdered in a hit-and-run by an Islamic-extremist-spouting convert in Saint-Jean-sur-Richelieu, Que., the shocking assault on Canada's Parliament immediately turned the national capital into a locked-down armed encampment.
Amid false reports of multiple shooters in multiple locations, Prime Minister Stephen Harper briefly hid in a utility closet before being spirited off the Hill. Later that evening, Harper would take to the national airwaves.
"In the days to come, we will learn more about the terrorist and any accomplices he may have had," a wan-looking Harper told the country, "but this week's events are a grim reminder that Canada is not immune to the kinds of terrorist attacks we have seen elsewhere in the world."
In the 12 months since, long-standing and well-recognized security gaps on Parliament Hill have been addressed and controversial new anti-terrorism legislation was enacted.
There have been no further attacks, no accomplices were ever found, and Canadians have learned precious little about what preceded the major intelligence and security breach.
And Harper's Conservatives, after running on a security-heavy platform, resoundingly lost government in a federal election this week.
Security expert Wesley Wark said that, in retrospect, Canadians showed "a remarkable display of public calm and resilience, which is precisely what you want in the event there is an attack of this kind."
"The resilience and the calm was all the more impressive in that these were the first terror attacks to have taken place in Canada since the advent of the 9-11 age," the University of Ottawa professor said in an interview Wednesday.
"I think it's important to remember that response."
On Thursday morning at the War Memorial, Harper, Gov. Gen. David Johnston, and prime minister-designate Justin Trudeau will be part of the commemoration, along with members of Cirillo and Vincent's families, soldiers from Cirillo's reserve regiment, first responders and police.
There will also be an eyebrow-raising 21-gun salute and a flypast by four CF-18 fighter jets, similar to Remembrance Day ceremonies.
The initial proposal for Thursday's ceremony, according to Defence Department sources, was for a simple wreath-laying accompanied by bagpipes. Other government departments got involved, proposing to bring Cirillo's regiment and family to Ottawa for the service.
Eventually the Prime Minister's Office stepped in, and Defence came back with the much more elaborate military display.
Michel Drapeau, a lawyer, professor and retired military colonel, said he learned of the military show when he was invited to the event.
"To have a 21-gun salute and a flypast, I'm asking myself, what for? And to what end? Are we celebrating something? Are we giving it too much importance and significance?" Drapeau said in an interview.
"To say the least, I'm surprised. I don't understand the logic of it."
A fierce critic of the Conservative anti-terror Bill C-51, Drapeau said the attack exposed woeful holes in Parliament Hill security — which have been addressed.
"But it is not sufficient cause to now adopt widespread changes that will in fact weaken, if not impair, our individual rights and freedoms," he said.
"We need to take a deep breath and say, 'Are we going too far?'"
For Ottawa Mayor Jim Watson, the anniversary is a chance to reflect on a tragedy but also the resilience of the city.
Rather than being frightened or cowed, citizens flocked to the memorial in the days after the shooting, he said.
In his office a block from the memorial, Watson has an original painting of Cpl. Cirillo standing guard. The artist also painted Cirillo's then five-year-old son Marcus into the frame.
As a fundraiser for the child, the mayor's office sold prints of the painting and raised $50,000.
"So we certainly responded to the personal side of the tragedy as well as the political side," said Watson.
He also praised the resistance to "knee-jerk" security responses in the national capital.
"We still have people playing rugby on the front lawn (of Parliament) and people taking yoga classes and tourists flocking up freely to the Centennial flame."
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