"...2015, when the exchange rate was still ok"

Right there you show you don't know anything. The exchange rate being "OK" ie. the 1 CAD was closer to 1 USD would not be an advantage to a physician returning to Canada. It would be a disadvantage.

With the Canadian dollar lower now it is more to the advantage of someone in the US selling their assets - home etc. - and moving to Canada. Those US assets are worth more compared to the Canadian equivalent now that the dollar has fallen. Income from US investments are worth more now when converted to Canadian dollars than if the Canadian $ was closer to par.

Similarly, selling your Canadian house, etc. and taking those Canadian dollars to the US costs you more now. Now that the CAD has fallen moving to the US is a more expensive proposition. And once you're there with both your income and expenses in US$ it no longer matters one way or the other what the exchange rate is.