I would recommend that the standing committee look at the jurisprudence of the Supreme Court of Canada to determine what the threshold for reasonableness is, because it would surely remain consistent regardless of the crime.
If we're talking about invading the privacy of an individual, normally a warrant is required in order to do that. Yes, there might be exceptional circumstances in certain cases, but the Charter of Rights and Freedoms is in place for a reason—to constitutionally protect those rights—and any infringement must be reasonable.
Simply saying that the collection of data relates to the functions of CSIS doesn't meet that threshold. Perhaps clearly demonstrating that there is an actual threat to national security may cross that threshold.