The government has already admitted that there's been evidence of tampering for over a decade now by China, though how significant of a swing that has isn't known. I'd like to think it was quite minor, but who really knows.
On the other hand, Russia is pretty famous for its botnet attacks on the US elections for a while now, basically early AI based attacks. Their fingerprints are all over twitter during the last several elections, not to mention the biggest driver of quite a few conspiracy theories.
This isn't a case of "very likely", but rather practically guaranteed. The question is whether the countermeasures will be effective enough or not.
Stepping down can sometimes be the real power move in politics, and for a politician that had quite few power moves for such a long tenure, this was one of Trudeau's.
And between the potential leaders, Carney is the only one that has a clear vision for the future on top of a plan to make it happen. While I don't agree with half of the stuff he's about, that's a million times better than a man more interested in causing division amongst Canadians when faced with an external threat, spineless coward that flip flops depending on what he things gets him political points, or people who have zero chance of gaining enough seats to make a serious change.