> Immigrants were brought in to fill that gap and pay for pensions and other goodies that expect a growing base of tax paying productive workers.

This is not true.

1) Immigrants are not brought in with the goal of topping up the numbers to the existing level, immigrants are being brought in with the intent of tripling the population. See https://en.wikipedia.org/wiki/Century_Initiative whose founders are advisors to the federal government.

2) Canada does not need immigrants to pay for its pensions. CPP and other pension in Canada are well run, invest their money, and don't just route money from young people to old. Rather, they pay the money out from the money already put in.