Your not getting the point.
So Canada does not allow foreigners to live there but work elsewhere.
Of course he can.
He is liscensed to practice in US, and is a US citizen, so he can work anywhere in US regardless of his status in canada.
Now, if he wants to practice in canada, he will have to meet whatever licensing requirement in canada as well as any immigration requirements.
I draw you a picture:
You want to nurse in Windsor, he wants to practice medicne in Detroit: You can either both live in Detroit, or he must apply for permanenrt residency in Canada (as your spouse, not as a doctor).
You both want to practice in Windsor. He can move to canada on a work visa (meeting all other medical licesnsing requirements). I do not know the licensing requirement s of US doctors moving to canada either temporarily of permanently.
But for him to live in canada, regardless of his profession or where it is practiced, he MUST get permanent residence. Again this would not stop him from working in US, since he is already licensed there.