Trump's threats to Greenland didn't stop the two longstanding main parties from falling to 3rd and 4th in their parliament. So the rally round the flag doesn't always help the incumbents.

I think part of it was that Canadians saw Carney as more credible than Poilievre, but they also have a trend for incumbent parties to improve their standing once writs drop. This has been true in both federal and provincial elections there for some time.