This will happen during the first caucus session that will include both elected MPs and those who were defeated.
Harper will accept the blame for the party's loss, but he will leave the full post-mortem of what went wrong to a committee struck by party on Oct. 20, Conservative sources have told CBC News.
Party president John Walsh has asked Dustin van Vugt, the Conservative Party's executive director, to initiate a transparent process to review the 2015 campaign in more depth.
After Harper speaks, members of caucus will have a chance to air their grievances and talk about what went right during the three-month election campaign, according to the sources.
Once that happens, a second meeting will be held of just the elected MPs.
That group will first vote on whether or not to accept the changes in the Reform Act, a bill that was put forward by one of their own, returning MP Michael Chong, and passed just before Parliament was dissolved for the election.
If the Conservative MPs choose to adopt the provisions of the Reform Act, only elected MPs would chose the interim leader — not senators.
Conservative senators have been lobbying to have some role in the selection of the interim leader.
Eight running to be interim leader
CBC News has also learned the interim leader will be chosen by a preferential ballot. Van Vugt will be the returning officer for Thursday's election.
There are eight people who have signalled they are interested in that job.
The list includes:- Ontario MPs Diane Finley, Rob Nicholson and Erin O'Toole
- Alberta MPs Rona Ambrose and Mike Lake.
- Calgary MP Michelle Rempel and Quebec MP Denis Lebel, in a joint bid
- Manitoba MP Candice Bergen.
In a posting to her Instagram account Sunday, Bergen said she has had calls with former MPs, newly elected members of Parliament and senators.
Also On HuffPost: