Canada's two newest astronauts will be announced at the country's 150th birthday party on Parliament Hill on Saturday.

Prime Minister Justin Trudeau and Navdeep Bains, minister of innovation, science and economic development, will introduce the astronauts onstage at the festivities around noon ET. 

Through a screening process that began last August, the pair have been chosen from an initial pool of 3,772 applicants who met the minimum criteria set out by the Canadian Space Agency. To qualify, candidates had to have a university degree in engineering, science, medicine or dentistry and be in "excellent health."

"We had to pick two, and I gotta tell you, it's tough," Jeremy Hansen, a Canadian astronaut who has been working in the space agency's recruitment program, told CBC News on Friday.  

Jeremy Hansen, Canadian astronaut

'We need people that we can put … in any situation and we know that nothing is going to faze them,' says Jeremy Hansen, an astronaut from London, Ont., who was recruited by the Canadian Space Agency in 2009. (David Donnelly/CBC)

"The two Canadians we picked are incredible. But if you told me we needed six, or 10, or 100 astronauts, there's no doubt in my mind we'd find them in Canada."

Hansen was one of the two candidates chosen the last time the Canadian Space Agency recruited new astronauts in 2009. The other was David Saint-Jacques, who is scheduled for a mission to the International Space Station in November 2018. Hansen's space mission is expected to happen sometime before 2024, but no details have been confirmed.     

The newest astronauts are two of the 17 finalists the Canadian Space Agency announced in April, after the candidates successfully completed gruelling physical and mental testing in Quebec and Halifax. The training exercises were designed to leave the candidates exhausted and frustrated, in order to evaluate how they performed under highly stressful conditions. 

"We need people that we can put … in any situation and we know that nothing is going to faze them," Hansen said. "They can work under extreme pressure, they can develop solutions when there isn't a black and white answer in front of them."

Since April, those 17 candidates have gone through extensive medical tests, as well as comprehensive panel interviews to identify important personal characteristics, Hansen said. 

"They have to be somebody I would be willing to be trapped in a tin can with for six months or a year," he said, referring to the tight quarters at the space station.

Canadian astronaut candidate

The candidates vying to become astronauts were put through a series of exhausting tests to challenge them mentally and physically to see how they functioned under stressful, unpredictable conditions. (Master Cpl. Chris Ringius/Canadian Space Agency)

Empathy and the ability to work as part of a team are among the key characteristics the recruiters were looking for, Hansen said.  

The 17 short-listed candidates are from B.C., Alberta, Manitoba, Quebec, Nova Scotia and New Brunswick and currently work as doctors, scientists, pilots, engineers and professors.  

The two chosen astronauts will begin two years of training at NASA's Johnson Space Center in Houston on Aug. 21, Hansen said. The Canadians will join 12 new American astronauts in the class.  

Spacewalks and Russian lessons

The astronauts will learn specific practical skills required in space, including spacewalks, operating the Canadarm 2 and how to operate and maintain systems on the space station. They will learn Russian so they can communicate with their Russian counterparts at the space station and also study planetary geology. 

"They have a lot to prove in the next two years. But we know that the two we picked are just going to do exceptionally well," Hansen said. 

Although it's not known when the new Canadian recruits will blast off on a mission, Hansen said being in space is only part of an "amazing job." 

"Ninety per cent of your career is going to be spent on the ground, training yourself, getting yourself ready for the challenges of space, which is significant and takes a lot of effort," he said. "But also, contributing to the space program, supporting your other astronauts who are in space at any given time.  And that's a great responsibility."

With files from Nicole Mortillaro