How much is this actually happening? I've heard plenty of anecdotes, but the net migration flows haven't changed much. British Columbia did a big push to bring in American medical staff, and have only had a couple hundred move so far. Compare that to the number of Canadians moving south on TN visas, and I'm not sure it's significant.

I am saying this as someone who pursued Canadian citizenship by descent and moved to New Zealand in the last year, so it's definitely happening some, but my impression so far is that the total number of people who actually make the move is small. Most people who are skilled enough for an overseas employer to jump through hoops to put them on a visa have more lucrative jobs available in the US that are closer to home without all of the downsides of emigration.

I would believe that a lot of dual citizens or skilled immigrants to the US are moving home.