The first explanation is that the PQ needs to play to its xenophobic base, as the CAQ might inherit its predecessor's xenophobic appeal. With sovereignty/secession not so popular these days, the PQ has to do much to emphasize the Us by targeting a Them--immigrants. Of course, this also helps mobilize the anti-Montreal folks since much of what goes on in Quebec is part of the Montreal versus everyone else dynamics.
But the problem is that this strategy by the PQ is in direct contradiction to its previous stance of reaching out to immigrants. Why reach out? Because if there were to be another referendum, the PQ would need votes from the new citizens of Quebec as well as the old ones in the hinterlands. The turn to xenophobia (especially its anti-Muslim themes) might be due to a realization that the French speaking immigrants may never want Quebec to be independent regardless of how nice the PQ plays.
Someone in Scotland suggested a longer term strategy--perhaps the PQ wants to drive out the immigrants, so that the potential No-voters are no longer an issue. The PQ and its policies have already done a nice job of alienating many Anglophones, leading to significant flight of those folks around the time of the last referendum (which meant that the house I bought in 2002 in Montreal was mucho cheaper than it might otherwise have been).
So, the short term strategy of solidifying the base might run against the long term strategy of making immigrants good Quebeckers and more likely independence voters, but may also play into a longer term strategy of producing greater homogeneity in Quebec. If Quebec becomes less diverse as Anglophones and immigrants leave, then Quebec separatists win.... even as Quebec loses. Yes, Quebec would be worse off if Montreal lost its diversity flavor not just economically but culturally as well.
But it has long been clear that what is bad for Montreal is good for the PQ: plus ça change, plus c'est la même chose. The more things change, the more they stay the same.