As large crowds gathered outside, the Duke and Duchess of Cambridge, as the couple is formally known, entered the Canadian Museum of Civilization, just outside Ottawa, and participated in a ceremony formalizing 25 people from 14 countries as new Canadians.
William presented each new citizen with a folded Canadian flag while Kate gave them a small hand flag.
The couple's entrance was heralded by the Sons of Scotland Pipe Band's rendition of a bagpipe piece, titled St. Andrews Courtship, created for the royal's visit, with the name a nod to the Scottish university where Kate and Will met and fell in love as undergraduates eight years ago.
While the duke and duchess welcomed new citizens, thousands of Canadians dressed in the nation's red-and-white colors gathered at Ottawa's Parliament Hill in anticipation of a celebration of Canada Day like no other.
Kate and William head next to Parliament Hill, the public grounds of Canada's parliament buildings, where they will arrivan in an open-topped, horse-drawn carriage for ceremonies marking their host nation's 144th birthday.
There they will be greeted by expected crowds of more than half-a-million and full military honors, including a 21-gun salute, and remarks from William and Canada's political leaders.
Later in the day, the royal couple will attend a public concert before moving on to a private diplomatic reception where they will watch a firework finale marking the national day.
Kate and William's celebration of Canada's 144th birthday comes the same day that William's mother, Princess Diana, who died in a 1997 Paris car crash, would have turned 50.
In London, Diana's admirers gathered to leave gifts outside Kensington Palace, which was her official residence and will be the home of Kate and William when they return from their overseas trip.
The Canada Day activities come one day after the duke and duchess received a rollicking, royal kick-off to their much-hyped North American visit.
After boarding the Royal Canadian Air Force aircraft at London's Heathrow Airport Thursday in coordinated outfits -- she in a blue shift dress and he in a blue suit and red tie -- the couple touched down in Ottawa where they were greeted by thousands of fans.
The duchess, wearing a navy-and-cream lace dress, got a rock-star reception.
"We want Kate," crowds chanted as the bride stopped to shake hands, accept roses and greet her fans gathered behind metal barriers.
"They're as close to A-list celebrities as the royal family can possibly get," ABC News royals correspondent Katie Nicholl said. "They're beautiful, they're glamorous."
William addressed his hosts in both English and French to huge cheers from the crowd.
"Catherine and I are so delighted to be here in Canada," he said. "Instilled in us by our parents and grandparents, who love this country, we have been looking forward to this moment for a very long time."
"Before we were married, we had a longing to come here together," he added.
Kate, who was not scheduled to speak and who has been heard from publicly only a few times before, joined her husband in expressing the couple's excitement.
"Thank you so much. We are so delighted to be here," she said.