I am afraid that from Australia, you do not see a few critical details.
In Australia, foreign-born are about 30% of the population. In Canada, it is about 20%. In the United States, legal immigrants are about 10% of the population, and we have illegal immigrants that are about 4% of the population, but no one knows for sure. Also, immigrant workers are about 17% of our workforce. Just from these numbers, one can see that our economy needs more immigrants that are allowed to come legally. The minimum, we need 15%-17% of legal immigrants to be a part of our population. As our economy operates in a similar environment as the Canadian one, our economy needs probably more legal immigrants, closer to that 20% in Canada.
Every illegal immigrant I know works here, despite that it is a crime to hire them. The economy needs them. Hence, Trump’s problem is not in trying to stop illegal immigration but choking our economy by restricting legal immigration. Why he does that? Listen to what he is saying.