To be fair, the Liberals wouldn't choose a voting system that would see them lose access to power, which PR would: there would never be another election where they could get 30ish% of the vote but win a majority, which suits them just fine: they'd rather change seats with the Conservatives every few years than be forced to compromise with other parties.

The electorate in this country is much more left-wing and progressive than the politicians it elects, and PR would codify that. The Calgarian and Laurentian elites wouldn't ever let that happen, which means that, if the NDP and BQ ever manage to form a plurality, they need to ram it through immediately.

And the Senate can pound sand: next to the Governors General, they're a useless rubber stamp anyway.