It would be exceedingly rare for one party to get enough votes to form a majority under PR.
But beyond that, we have the non-partisan senate, the governor general, and the Charter (via the judicial branch) to all act as obstacles to unjust legislation. Canada is no stranger to majority governments under our current system, and the checks 'n balances have worked pretty well so far, for the most part.
Barring a trump-style lunatic jacking up the executive branch (which can absolutely happen, that's something us citizens have to be careful not to vote for), PR should make it slightly harder for tyranny of the majority to happen. Take a look at New Zealand in 1996 for a relatively recent example of PR adoption and how their voting patterns have changed after the switch.