Regarding PR, there is no reason for the Liberals to support it. There is a good chance it will go to parties heavily controlled by the leader, which is bad.I think most people will find that ranked ballot will favour the Liberals. The only party that overwhelmingly benefits FPTP is the Conservative party.
If you didn't know, Trudeau favours ranked ballot and it would have put the Liberals in power for perpetuity unless there was a big change where every party worked together to vote them out. https://www.cbc.ca/news/politics/trudeau-electoral-reform-1.3976345
You only have to look at the Conservative leadership results as an example of what would likely happen, in a ranked ballot, or instant runoff type voting system. Basically, the least offensive choice will win out in the long run as being the perpetual second choice. Assuming that most ridings have 3 main contenders (Conservatives, NDP, Liberals), when it comes down two it, would most Conservative voters rank NDP above Liberals? Or would most NDP voters rank Conservatives above Liberals? I'm sure there are some exceptions, and only in an extreme case where the Liberal party has universally alienated the whole population, where it is unlikely that the Liberals are the preferred 2nd choice.
As for PR, it's more likely you'd get a pizza-style parliament like in most European countries rather than coalescence into 2 parties.
Edit: An article where they simulated a ranked vote result in 2019 election based on a survey of preferred 2nd choice. The Liberals and NDP would have gained while Conservatives and Bloc lost seats. Who wins Election 2019 under a ranked-ballot system - Macleans.ca
As far as Ranked ballot, many people vote Liberal as a protest against the Conservatives.
I think that, after an adjustment period, there will be more groups and candidates with more nuanced positions.
Given the choice between the Liberal party, and a party with the same policies, just less racist, I can imagine that former Liberal party voters would be glad to put that new party as 1, with the old party as 2.
That's the real risk to the established parties.
Look at the US, sure there are real Trump supporters, but really 2020 will be a repeat of 2016, where most people were just voting "against" the other guy.
On Ranked ballot they could have easily put in someone who wasn't as bad as Trump or Clinton (now Biden), and they would have gathered a LOT of #1 votes.