Liberal Leader Justin Trudeau and NDP Leader Tom Mulcair will speak to reporters after their parties meet.
CBC News will have Mulcair LIVE at 11 a.m. ET and Trudeau LIVE at 12:30 p.m.
The Conservative caucus is also meeting Wednesday morning.
On Tuesday, Duffy, the former Conservative senator, spoke publicly for the first time in months, following a summer of allegations in RCMP court documents that he misspent Senate funds.
Duffy alleged for the first time that when Nigel Wright, Harper's former chief of staff, arranged to repay Duffy's questionable expenses — a total of $90,000.
Duffy also named names of people involved in negotiating the alleged arrangement and in putting pressure on him, he says, to repay the expenses.
Duffy says he hasn't done anything wrong and that his housing claims, some of the spending for which the RCMP are investigating him, are above-board.
Each party meets every Wednesday when Parliament is in session, leading to raucous question periods afterward. CBC News will have question period LIVE at 2:15 p.m.
Senator Patrick Brazeau, who has also been hit by the spending scandal, spoke to the Senate on Tuesday. Senator Pamela Wallin will speak to the Senate this afternoon.