https://www.cbc.ca/news/politics/csis-rcmp-data-access-telecoms-9.7148631
"... so that [cops] can search the haystack for the needle so to speak, if the need arises."
Or, historically speaking, find a needle-shaped piece of hay after-the-fact and follow a "gut feeling" that it's actually a needle.
With what I know about Stingrays/IMSI catchers, cops need the data the feds propose retaining in order to use them for more than "was this person at this location." It will probably end up involving Palantir contracts.
Fuck that.

Liberal bill would force companies to simplify data access for police. No one knows the cost | CBC News
The Liberal government's second attempt at giving police and spies easier access to Canadians' information includes what's anticipated to be costly demands on a range of private businesses to to change how they manage their data.