It wouldn't be a conspiracy, just strategic thinking.
It wouldn't be the first time in history where one party/group/individual decides to relinquish power anticipating some crisis:
- Sulla was a dictator who retired before the collapse of the Roman republic.
- The British handed over power to India before the communal violence escalated.
- Nixon resigned to avoid the spectacle of impeachment.
Someone in power may be able to better see some things inevitably coming and bail out sooner to avoid the worse.
You said Trudeau was unpopular for years and yet only now he's leaving.