The opposition party caucuses gathered Wednesday morning, while the Conservatives seemed to eschew their weekly meeting, after the House agreeed Tuesday night to break for the holidays.
Liberal Leader Justin Trudeau will speak to reporters at 12:15 p.m. ET.
New Democrat MP Alexandre Boulerice said Canadians will take away from this session that it's hard to tell whether Harper is telling the truth.
"There are plenty of versions of the same story, he isn't capable of telling the truth to people," Boulerice said of Harper, in a scrum on Parliament Hill after his party's meeting.
"We question seriously whether the prime minister is telling the truth... I think the RCMP will continue to do their work."
Affidavits filed in Ottawa court show the RCMP are investigating Duffy and Nigel Wright, Harper's former chief of staff, for fraud, bribery and breach of trust. No charges have been laid and the allegations haven't been tested in court.
MPs will return to their ridings for the next six weeks, with the House expected to return Jan. 27, 2014.
Senators usually rise a few days after the House.