Justin Trudeau is the leader of the Liberal Party of Canada as of the time of writing this question.
When Justin Trudeau ceases to be leader of the federal Liberals, who will replace him?
This question resolves to a named individual and not to “Other.” Acting or temporary leaders do not count. The resolution date will be extended as necessary until Justin Trudeau is permanently replaced.
See also:
CBC podcast Front Burner recently put out an episode on whether Trudeau will stop being Liberal Party leader before the next election.
The interviewer, Jayme Poisson, and the guest, David Herle, also discuss potential successors.
I've added Sean Fraser and Dominic LeBlanc since they were brought up in the conversation and weren't among the options before.