Prime Minister Justin Trudeau said intelligence agencies and police forces were doing “everything necessary” to keep Canadians safe for the country’s 150th anniversary, as concrete barriers were placed near Parliament Hill to prevent any potential ISIS-inspired vehicle attacks.

“I want to make sure that people are at ease,” Trudeau said Wednesday during a trip to Toronto. “Every year we step up around Canada Day to ensure that everything is done to keep Canadians safe.”

Trudeau’s comments came after a national security memo obtained by CTV News outlined a warning from ISIS that “explicitly named Canada” and the United States as possible targets after the Manchester attack in May.

With a massive crowd of 500,000 expected to flock to Parliament Hill, heightened security measures will be on place throughout Ottawa on Saturday.

Canada’s elite counter-terrorism response unit will be on standby this weekend for the highly-anticipated Canada Day celebrations in the capital.

Joint Task Force 2, or JTF 2, is an arm of the Canadian Forces that combats terrorism at home and overseas. Sources say the highly-trained unit helped develop security preparations for the Ottawa event.

Snipers from the RCMP Emergency Response will also be at the ready, and attendees can expect to see heavily-armed officers and security cameras strategically positioned throughout the event.

Roads are also being shut down days earlier than usual to prepare for the event.

The multifaceted safety precautions are part of co-ordinated efforts by intelligence officials, law enforcement and the government to make sure that the party runs smoothly.

Security efforts are similarly being ramped up in cities across Canada. Some communities have called in extra first responders and police officers who initially had Canada Day off.

In a statement to CTV News, the military says it has troops ready to deploy across the country if need be.

Stephanie Carvin, an assistant professor of international affairs at Carleton University, says ISIS is known to look for “soft targets” – vulnerable public areas that are densely populated and difficult to protect.

Even so, Carvin says security preparations for Canada 150 have been thorough.

“The prep for this event didn't start last week. It didn't start after the Manchester attack. It started over a year ago,” she told CTV News.

The government understands the need to be “attentive and vigilant,” Trudeau said, and authorities are continuing to work closely with security officials leading up to the event.

“We will do -- as we do every year -- everything necessary to work with our police agencies, our national security agencies to ensure that Canadians celebrating in Ottawa and indeed right across the country are as safe as they can be,” Trudeau said.

‘I hope this will not scare people away’

In an interview with CTV’s Power Play on Wednesday, former CSIS director Richard Fadden said Canadians shouldn’t let fear overshadow the spirit of celebration this weekend.

“I hope this will not scare people away from having a good time. Because if we start changing the way we do things because of this, they will have gained some measure of success, and that’ll be awful in and of itself,” Fadden said.

Terrorism has two components, Fadden says: actual acts of violence carried out against innocent people, and baseless threats intended to stoke fear.

“The problem is, you never know which of the two you’re absolutely having to deal with,” he said.

In his time leading Canada’s intelligence agency, Fadden said security efforts were carried out with detailed co-ordination. Intelligence officials worked closely with hospitals, fire officials and police to make sure everyone was “on duty and ready to help if need be” in the event of a threat.

Fadden said he expects a similar all-hands-on-deck approach in Ottawa this weekend.

“I think they’re doing all the basics, which is restricting access by automobiles and motorcycles, they’re having a station to check people before they go in,” he said.

The key to success, he says, is what’s going on under the radar, such as how many undercover agents are on the scene.

“We do this not only because there are terrorist groups, but occasionally when we have a very, very important foreign visitor. So they’ve good at it. The difference, I think, for this weekend is going to be the numbers. There are going to be a lot of people.”

ISIS playing ‘mind games’

ISIS has made threats against Canada in the past, and so news of the latest threat is “all part of the mind games that they play,” said Michael Zekulin, a terrorism researcher at the University of Calgary.

“It’s just part of their larger game plan that they’re going to suggest that this is imminent,” Zekulin told CTV News Channel.

Large crowds gathered for celebrations have been targeted in recent ISIS-inspired attacks: the suicide bombing at an Ariana Grande concert in Manchester, the Palm Sunday bombings at two churches in Egypt, the Istanbul nightclub shooting in January.

“Unfortunately we know that these large gatherings, these public places with lots of people, tend to be the more desirable targets right now. We’ve seen this repeatedly,” Zekulin said.

“These are the types of things that [ISIS terrorists] like to do. It does not, however, necessarily mean that they have the ability to actually inspire somebody to do that.”

Zekulin said he expects intelligence officials are working “below the radar” in the lead-up to Canada Day to detect any potential threats. He says Canadian officials are likely working with intelligence partners and keeping close watch on online “chatter.”

“You’re just basically crossing your T’s and dotting your I’s to make sure you’re doing all you can,” he said.

Witha  report from CTV's Mercedes Stephenson in Ottawa