"No constitutional amendment is required for Canada to give its assent to this U.K. legislation, and we are prepared to defend the Succession to the Throne Act, 2013 before Canadian courts," Paloma Aguilar, spokeswoman for Justice Minister Peter MacKay, said Monday.
The legal posturing, a harbinger of a potential constitutional spat, erupted as Prince William's wife, Kate, gave birth to a boy, now third in line to the British throne.
The revamped succession laws would have had more application had the new royal baby been a girl because they modernize the previous rule of succession that allowed younger boys to leapfrog over their older sisters. Parliament passed Canada's law in March.
Canada joined 16 other Commonwealth countries, following a British request, to fast track royal succession laws.
Last month, two Quebec professors filed a constitutional challenge of the Canadian law in Quebec Superior Court because the provinces were not consulted.
Initially, the province of Quebec did not immediately align itself with the legal action.
But that changed hours after reports emerged that the Duchess of Cambridge had gone into labour on Monday.
A spokesman for Quebec's attorney general told The Canadian Press via email that the province is "effectively" in the case.
Paul-Jean Charest said the department would soon file a legal motion before the courts, and would make its position known then.
Montreal lawyer Andre Binette, who represents the professors, said he expects the Quebec government to back his case.
"We now think they will. We've kept them informed of various developments. At first they said they wouldn't come in, but now they changed their minds," Binette said in an interview.
"They will take a position, which I presume will be in support of ours. I can't see them taking another position at this time."
Binette said the parties will be in court Aug. 15 to map out the way forward.
He said there are two scenarios. The longer one would see the case argued before the current trial court, before wending its way to the provincial court of appeal, and eventually the Supreme Court of Canada.
That could take three to four years, perhaps longer.
Binette said he was hoping Ottawa would exercise its discretion and refer the case directly to the Supreme Court for an opinion, which would be a much more speedy resolution.
MacKay's spokeswoman appeared to dismiss that fact-track option.
"As you know, the matter is before the Quebec Superior Court, and it will proceed according to its rules," said Aguilar, saying she could not comment further.
Binette said he plans to call at least half a dozen expert witnesses on Commonwealth and constitutional issues from across Canada, as well as from Australia and New Zealand.
Robert Finch, dominion chairman of the Monarchist League of Canada, said Monday he was aware of these legal developments.
He said he support Canada's position, but lamented the timing of the discussion.
"The overwhelming majority (of people) are simply excited about the royal baby and aren't getting too caught up with the legal nuances," he said shortly after learning of the Quebec government's intervention in the case on social media.
"I'm surprised the Quebec government is coming late to the table to challenge it," he added.
"The timing is kind of dreadful, but hey, that's the nature of the beast."