Well it does a pretty remarkable job. Recall too that the stats are foreign born as a percentage of the population (Peri, 2016 that I mentioned above).
The USA is larger than all Canada, Australia, UK and NZ combined. So, let's not pretend that the US is not taking new comers at all. We're still in the ballpark of close to 50 million people. This compares to about 7 million in Canada.