About 35 protesters, including members of the separatist group Reseau de Resistance du Quebecois, or Quebecker Resistance Network, stood outside Sainte-Justine University Hospital Centre in Montreal chanting "A united people will never be vanquished."
They carried signs that read "Parasites go home," "War Criminals," and "Your fortune came from the blood of our ancestors."
"It's a symbol of English dominance over Quebec," said 30-year-old lawyer Antoine Pich of the couple's visit.
Dressed in black capes, the protesters were drumming and booing as the royal couple's motorcade pulled up to the hospital. William was whisked into the hospital as Kate stepped out of the car and smiled at the crowd before going in.
The demonstrations were a rare moment of criticism aimed at the young royals, who have for the most part been welcomed with open arms by Canadians eager to catch a glimpse of the glamorous newlyweds.
The protesters were outnumbered about 10 to one by William and Kate supporters gathered outside the hospital. "Give me one good reason why you should hate someone. They're good people," said Elyane Lafontaine, 51.
Saturday was the couple's quietest and least frenetic day since beginning their tour on Thursday. The trip unfolded with two days of rousing crowds and seas of well-wishers clamoring to catch a glimpse of royalty during the couple's stay in Ottawa, the country's English-speaking capital city.
The newlyweds were there to visit with cancer patients and the hospital's neo-natal care facility. The Sainte-Justine University Hospital Centre is the largest mother-child center in Canada.
Protesters were angry that Canada still has ties to the monarchy. Queen Elizabeth II is still the country's figurative head of state and new Canadian citizens still pledge allegiance to the Queen during their swearing-in ceremony.
Michael Behiels, an Ottawa University professor, said there was much hostility between the French and the English in the years following Great Britain's 1759 Conquest of New France - which is present day Quebec.
The continued presence of the monarchy atop Canada's constitutional order is a reminder, after 250-plus years, that the country's two founding countries formerly waged war against each other.
Others said they were angry that taxpayer money is being used to pay for the royal tour.
Maxime Laporte, head of the Reseau de Resistance du Quebecois, said the monarchy doesn't represent Quebec and is illegitimate here because the province has never accepted Canada's constitution. He called the royal tour a "nation-building exercise" funded by taxpayers.
The royal couple left the hospital and headed to the Inistitut de Tourisme et D'Hotellerie du Quebec, where they were met once more with a handful of protesters who were again dominated by about 150 supporters. Some spectators held signs that said, "Bienvenue Will et Kate sur Le Plateau," which welcomes them to the trendy Montreal neighborhood where the institute is located.
Kate and William donned aprons and took part in a cooking workshop at the facility, which is a government agency that conducts training and research in the hotel, tourism and food service industries.
Quebec has always been the most vocal anti-monarchist province in Canada.
Before heading to the French-speaking city, the Duke and Duchess of Cambridge started the third day of their tour in Ottawa, Ontario, with a tree-planting ceremony at Government House that has become a royal family tradition and a visit to the Canadian War Museum.
Saturday's small, low-key gatherings in Ottawa contrasted with Friday's celebration of Canada Day when Prince William and Kate stole the show as they were feted by Canadian leaders and cheered by tens of thousands who lined the streets to get a glimpse of the royal couple.
Prince William, wearing a dark blue suit, and Kate, dressed in a grey, fitted knee-length Kensington dress by British designer Catherine Walker, each wielded a shovel as they helped plant a Canadian hemlock - a tree known for its longevity meant to symbolize their marriage.
Their tree was the 17th planted by a member of the British royal family in a tradition dating back to 1939. Prince William's parents, Prince Charles and Princess Diana, and his grandmother, Queen Elizabeth II, planted trees on previous visits at Rideau Hall, the official residence of both the Canadian monarch and Governor General, the queen's representative in Canada.
The royal couple chatted with Canadian newlyweds who were married on April 29, the same day as their royal wedding, as well as couples celebrating their 40th, 50th, 60th and 70th anniversaries.
William asked CB Marsh, who recently celebrated his 70th anniversary with his wife Edna, asked what advice he could give him. "I told him the ability to duck. He seemed to enjoy that," the 94-year-old Marsh said.
The royal couple also met Terry Joyce, 47, who has terminal cancer. Joyce was told six weeks ago that he had 12 weeks to live and said it was one of his last wishes to meet the couple.
"They were very comforting," he said.
The couple then attended a reception at the Canadian War Museum with veterans of conflicts from World War II to Afghanistan. The couple met with the veterans and with war brides - about 45,000 women came from Europe to Canada as war brides after World War II, most of them from the United Kingdom.
Moments after entering the museum, the couple walked over to a group of seated women who served as nurses in the Canadian military during World War II and the Korean War. The royal pair spent several minutes with the women.
Some in the room pulled out photos to show the couple, likely taken during the conflicts, as William and Kate listened attentively to their stories. Others handed them flowers.
The royal couple are in Quebec for a two-day stay.
The Reseau de Resistance du Quebecois planned a larger protest outside city hall in Quebec City on Sunday, with supporters coming in by bus from other parts of the province, said RRQ spokesman Julien Gaudreau.
A 2009 visit by Prince William's father, Prince Charles, to Montreal was disrupted by more than 200 separatist protesters. The protesters sat in the street, blocking the prince's way into a ceremony planned at an armory, and threw eggs at the soldiers who were accompanying him and his wife, the Duchess of Cornwall. The couple were forced to enter the building through a back door and missed an elaborate welcoming ceremony that had been planned.
Prince William's grandmother, Queen Elizabeth II, found herself in the eye of a Quebec nationalist storm during a trip in 1964. As she toured Montreal, helmeted police officers clashed with several hundred boisterous marchers, who flashed obscene, two-finger "V" signs at the young monarch.
In 1990, Canada Day celebrations were disrupted briefly by protesters from Quebec who booed and turned their back on the queen.
However, support for the separatists among Quebeckers has been on the decline in recent years as the 80-percent French-speaking province has enjoyed plenty of autonomy even without quitting Canada.
The royal couple leave Canada for a three-day trip to California on July 8.
Associated Press Writers Charmaine Noronha in Toronto and Rob Gillies in Ottawa, Ontario, contributed to this story.