Marleau-Montpetit notes the following:
A committee may wish to hear testimony from private individuals, representatives of groups, or public officials concerning the matter which it is studying. Witness selection may be carried out in a number of different ways. Normally, witnesses are proposed by individual committee members. The committee may also invite potential witnesses to indicate their interest in appearing. The selection is often delegated to the Sub-committee on Procedure and Agenda, subject to ratification by the full committee.
It is the responsibility of the committee as a whole to determine which witnesses it will hear. Practical considerations, such as the length of time allocated for a study, limit the number of witnesses the committee will be able to accommodate. While any member of a committee may propose witnesses, the committee makes the final decision as to who will be heard.