The Five Eyes and India have been communicating about this for a couple months now, but Trudeau publicly announced this after The Globe and Mail said they would publish a story about Foreign Interference. To preempt that Trudeau announced this in Parliament 30 minutes before that article was released [0]
Generally, stuff at this level is highly sensitive and classified because it becomes a headache for everyone [1]. It doesn't make sense for the Canadian PMO to leak this despite G20 crap because it has no actual benefit during a non-election year nor does it make sense for the Indian PMO to leak this as this impacts Indian foreign relations.
Was this a disgruntled CSIS analyst (like the China Election Interference leak), the Tories (they leaked the existence of a military base in Afghanistan used for anti-Taliban black ops), disgruntled NDP MPs (force an early election and win the Vancouver suburbs where they compete against the Liberals), or disgruntled Liberal MPs (force an early election and get a cabinet position or a more senior role)?
[0] - https://www.cbc.ca/radio/asithappens/harjit-sajjan-hardeep-s...
[1] - personal experience