Wouldn't work.
It would have to be a split tax, between employee and employer.
And the tax would need to be enormous, because many people will decide to retire early, rather than work and pay the high taxes...
And why not retire early, if you have guaranteed health benefits paid for by your rich Uncle Sam?
Any way you slice it, the economic mess will be giant.
Overtaxed Canadian nationals will stop working in the USA and go home.
In the short run there would be a worker shortage. Wages would increase, and there would be stagflation: the economy would shrink while inflation goes on a rampage.
Support Hillary!!! Bring it on!!!