I could see Chrystia Freeland being another possibility. She is of Ukrainian descent and has taken a very hard line on Ukraine. She is generally well respected in establishment circles. And with Trudeau not likely to step down before election and party likely to lose this would be a good exit. Main problem for her is Canada is one of the furthest from committing 2% of GDP to defense spending.
Freeland was mentioned as a possibility last year but seems like there was a consensus that the candidate should be European, plus Canada's lack of defence of spending you mentioned also hurt her chances.