Unless you believe in zero immigration which you absolutely have the right to, the material reasons for when immigration is bad for workers are the lesser workers rights they have and the shortage of housing and transit. Workers rights because unionized workplaces mean corpos can't pay a migrant less than a Canadian, therefore have little incentive to bring them in. And if they do so in a non-unionized workplace, the migrant worker has the economic means to switch jobs, which means the corpo has to pay them similar to Canadian labour. And housing and transit are about the only limited resources standing in the way from scaling up any Canadian town or city from its current size to virtually any size. If we get housing and transit building so that we don't have those constraints, and new people entering the economy aren't at permanent worker rights disadvantage, like new Canadian grownups aren't, then the economic effects should be more or less equivalent to natural increase in the population, which tends to be economically positive. Better yet, the economy should benefit more than natural pop growth because Canada didn't spend the resources raising and educating this new population, while we'd get the surplus it produces as it enters the workforce.

If immigrant labour does not have the same rights (including recognition of experience, education through some process, etc) as non-immigrants, then the only way to not have corpos use them to lower wages is to not let them in at all - or zero immigration. But new workers constantly enter the workforce in a growing population as kids grow up so the mere entry of new workers into the economy doesn't appear to be bad for wages. The baby boom along with strong workers rights (much weakened later) produced a pretty great economy for working people.

If you're worried about giving workers real power, the NDP is not for you.