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.
The royal couple traveled directly from the airport to the National War Memorial, where they were met by Prime Minister Stephen Harper and his wife, Laureen. Kate and William each laid a wreath at the memorial and stepped into the crowd to speak with veterans.
Even rain later in the day did not dampen spirits. More than 120 young Canadians turned out for a barbecue in their honor that had to be hastily brought inside due to bad weather.
The bad weather also didn't dampen Kate's style. The fashion-plate duchess had three separate dress changes on just the first day of the 10-day tour, for which she reportedly brought 40 outfits.
Kate welcomed the new Canadians on Friday in a crisp white dress, red pumps and red maple-leaf pin, a nod to the nation's symbol.
"It's been a great wardrobe for a great kickoff of the royal tour," royal expert Nicholls told ABC.
The royal trip is Middleton's first visit to Canada; William has traveled there before. The trip will be closely followed by the media, with nearly 1,400 journalists accredited to cover the visit.
The country, a member of the Commonwealth whose head of state is Queen Elizabeth II, William's grandmother, also created a personal flag for Prince William to mark the visit.
The flag, unveiled by Canada's prime minister and approved by both the Queen and William, is the first to be created by Canada for a member of the royal family since 1962, when the queen adopted a personal flag for her own use in Canada.
The flag, featuring three maple leaves, will from their cars and all buildings they visit or stay in during their trip.
Royal Trip Guide
After Ottawa, the royals will travel to Canada's sole French-speaking province, Quebec, on Saturday, July 2, via an overnight cruise ship.
There they will participate in a series of events typical of a royal, goodwill tour, from meeting with veterans and their families, to touring a maternity center and attending a tree planting ceremony.
On Monday, July 4, the couple will arrive in Prince Edward Island where William, a member of the Royal Air Force's search and rescue force, will show off his skills by participate in a training session for an emergency sea landing by the same Sea King helicopter he flies back home in Britain.
The duke and duchess then head to Canada's rugged Northwest Territories before arriving at their final stop, Calgary, which could be the most down-home, and most lively, stop on their tour.
Look for Kate's trademark, British headwear to be replaced by a cowboy hat when she and Will attend the Calgary Stampede, the world's largest rodeo and self-proclaimed "Greatest Outdoor Show on Earth," and kick off the Calgary Stampede Parade, the second largest parade in the world.
That afternoon the couple will say farewell to Canada, and hello to America.
The duke and duchess' visit to America will take them to only one state, California, and their short weekend stay in the Los Angeles area is being highlighted by their handlers as a working visit, not a time to mix with celebrities.
"The palace is really playing down any big introductions to A-list stars," ABC News royal correspondent Katie Nicholl said. "These tours are fun but hard work. It's really about forging ties between America and Great Britain."
The Royal "Nontourage"
Prince William and Kate's philanthropic-focused itinerary and scaled-down entourage for their North American visit are a sign of the couple's determination to keep their royal life as modest as possible.
Following their fairy tale wedding at London's Westminster Abbey on April 29, William returned to work as a search-and-rescue pilot in Anglesey, while Kate was seen grocery shopping for the couple herself.
Traveling without a personal dresser, or lady-in-waiting, the duchess will rely on her longtime London hairdresser, James Pryce, who styled her wedding and engagement hair, for both fashion and hair advice.
One area of help where the couple did not scrimp is media, bringing along a number of experts to help them handle the expected crush of press.
ABC News' Luchina Fisher and the Associated Press contributed to this story.