CBCNews will carry Mulcair's scrum live at 11 a.m. ET.
Liberal Leader Justin Trudeau is planning to speak with reporters at 12 p.m. ET.
The two parties waged hotly-contested byelection campaigns in Montreal and Toronto over the past month, which saw the Liberals retain both seats. Some NDP officials and supporters were upset by Trudeau's invocation of late NDP leader Jack Layton's final letter to Canadians at a victory rally in Montreal on Monday.
CBCnews.ca will carry both press scrums live.