Unusually high early turnout is a bad omen for the incumbent

Not really. A quick Google search and you will see that for the last six elections the number of early voters increased every time.

• 2008 -> 1.5 million early voters -> Harper won
• 2011 -> 2.1 million early voters -> Harper won
• 2015 -> 3.7 million early voters -> Trudeau won
• 2019 -> 4.9 million early voters -> Trudeau won
• 2021 -> 5.8 million early voters -> ????

https://www.elections.ca/content.aspx?section=res&dir=rep/off/sta_2011&document=p2&lang=e