Ontario's numbers are huge but important to throw an asterisks on all this analysis with some per capita measures and longer term trends. Per capita, the territories, Saskatchewan & Manitoba have a far more significant out-migration pattern than Ontario for many years, and remain so. International immigration to Ontario offsets interprovincial losses 15 times over.Re: Ontario
I posted a few interprovincial migration graphs below. What jumps out to me is actually how consistent Ontario's numbers actually are. Remarkably, ins/outs have stayed to about 20 - 30,000 a year on a population of 15 million. The fact that Alberta's inter-provincial ins/outs are often larger in absolute magnitude than Ontario, despite having less than 1/3rd the population is revealing about our economy.
The other thing that surprises me is absolute interprovincial migration isn't really changing much over 20 years despite a much larger Canadian population. Yes, some years are higher than others, but the total amount of movement looks to be hardly moving for most provinces. I would have thought migration per capita would likely stay constant, instead it seems absolute migration is staying relatively constant (meaning per captia it's decreasing as our populations grow).