Canada passed 40 million population this year and will hit 41 in a few months.
A large percentage of immigrants are becoming pregnant the year they immigrate. Let's assume there is no interaction with the native population. For the example's sake, let's assume 500k is evenly split men and women. let's assume 40% of the immigrants have a child in the first year.
Total immigrants divided by gender times 40% percent having a child in the first year: 500k / 2 * 0.4 = 100k
That means a theoretical 500k immigration rate is actually 600k after one year.
And, in fact, for the hypothetical sake assume the same thing happens in year two as the original women have a second child in year 2 and now the original population has become 700,000.