https://www.canada.ca/en/democratic-institutions/services/protecting-democracy/critical-election-incident-public-protocol.html
The Critical Election Incident Public Protocol (the Protocol) lays out a simple, clear and impartial process by which Canadians should be notified of a threat to the integrity of the 2019 General Election.
The Protocol includes provisions for: informing candidates, organizations or election officials if they have been the known target of an attack; briefing the group of senior public servants at the heart of the Protocol; informing the Prime Minister and other party leaders (or their designates) that a public announcement is planned; and notifying the public.
The Prime Minister cannot veto the decision to notify Canadians of a critical incident