The Duke and Duchess of Cambridge could be headed to Canada if the prime minister's invitation is accepted.

Justin Trudeau has formally asked Prince William and his wife, Kate, to consider crossing the pond for a royal tour with the family, including their two young children, Prince George and Princess Charlotte.

"A letter of invitation was sent to their royal highnesses." said Andrée-Lyne Halle, a press secretary for the Prime Minister's Office.

"The PM has invited them to come to Canada whenever their schedule permits it," Halle said, adding "there are no confirmed dates for the moment."

If the royals accept Trudeau's invitation, it will be their second trip to Canada as a married couple but their first since becoming parents.

Crowds look on as the Duke and the Duchess of Cambridge take part in Canada Day festivities on Parliament Hill in Ottawa on Friday, July 1, 2011. (Sean Kilpatrick/Canadian Press)

William and Kate last visited Canada in 2011 as newlyweds, attracting hundreds of thousands of spectators during their nine-day tour.

The royal couple visited seven cities and five provinces, including P.E.I., Alberta, the Northwest Territories, Quebec and Ontario, with a stop in Ottawa to mark Canada Day on Parliament Hill.