About 500,000 people were expected to be in Ottawa for the long-anticipated Canada Day festivities, which features a large outdoor celebration in front of the national Parliament, complete with acrobats, fireworks and musicians, including singer Bono and other members of Irish rock band U2.
Trudeau, accompanied by Britain's Prince Charles, shook hands with some of the thousands of revelers who converged on Canada's capital Ottawa for the festivities.
"Canada is a country made strong not in spite of our differences but because of them," Trudeau told the gathering. "We don't aspire to be a melting pot - indeed, we know true strength and resilience flows through Canadian diversity."
Some cities are celebrating in more unusual ways. Toronto, Canada's largest city, will have a giant rubber duck floating in its harbor, while Calgary will have a "living flag" composed of people wearing red and white.
Security was already ramped up in the days ahead of the celebration and party-goers must contend with road closures and concrete barriers across entrances into Parliament Hill, located in downtown Ottawa.
National and local police were also out in force, with security top of mind for many Canadians in the wake of fatal attacks in London, Paris and Germany.
Saturday marks the 150th anniversary of the day Canada officially became a country. Britain had ruled it before 1867.
The nationwide party comes as Canada is enjoying an unusual amount of interest from the rest of the world, largely due to the election of charismatic and selfie-prone leader Trudeau.
Still, in the runup to the celebrations, some controversy was stirred at home, particularly among First Nations who noted Canada's history of mistreatment of indigenous people. Activists erected a teepee on Parliament Hill on Thursday in protest.
"As a society, we must acknowledge and apologize for past wrongs, and chart a path forward for the next 150 years," Trudeau said in a statement ahead of the official kickoff.
Indigenous rights group Idle No More has called for a national day of action on Saturday, telling supporters to hold rallies and take to social media.
Events and installations celebrating the sesquicentennial milestone have already been held across the country this year, with the total cost to the federal government reported to be half a billion dollars.
Along with fireworks, free museums and outdoor concerts nationwide on Saturday, more than 50 special ceremonies to swear in new citizens will be held across the country.
Twitter users were sharing their favorite Canadian songs and food, along with photos of the preparations under the hashtag Canada150.
Prince Charles and his wife Camilla arrived in Canada for an official visit on Thursday. The royals began a three-day tour of Canada with a trip to the northern territory of Nunavut, home to a large number of First Nations and Inuit people.
The bash in Ottawa will culminate with a musical fireworks show that is billed as largest-ever such display for Canada Day. It will last for 20 minutes and 17 seconds to commemorate 2017.
(Additional reporting by David Ljunggren in Ottawa; Editing by Denny Thomas and Matthew Lewis)
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)