You have to take into consideration the concept of domicile, which is not the same as residence. Here's a good explanation of domicile, which happens to be from the Idaho State Tax Commission web site. But the definition of domicile does not change from state to state.
Domicile
Your husband's domicile is not North Dakota and it is not Idaho. From what you've said, it seems that his domicile is in Canada, where you live.
The definition of a resident does vary from state to state (and the definition of a resident for income tax purposes could be different from the definition for other purposes). Here's a link to the Idaho definition of a resident for income tax purposes.
Idaho Residency Status
As you can see Your husband is not an Idaho resident. He does not have a home in Idaho, and Idaho is not his domicile. Having an Idaho driver's license and getting mail at his parents' address do not make him a resident. There is no reason for him to file an Idaho tax return.
Here's a link to the North Dakota definition of a resident for income tax purposes.
Who is a resident for North Dakota individual tax purposes?
You can see that your husband also is not a North Dakota resident. North Dakota is not his domicile, and he does not have a "permanent place of abode" there. But since he has income from working in North Dakota, he has to file a North Dakota nonresident tax return and pay North Dakota tax on the money that he earns there.
He is probably a Canadian resident, since Canada seems to be his domicile. Therefore he probably has to file a Canadian tax return. But neither I nor anyone else here in the U.S. TurboTax community is familiar with Canadian tax laws. There is also a tax treaty between the United States and Canada that might come into play. You might want to ask for help in the TurboTax Support Community for Canada. But since your situation is so unusual and complicated, it's probably better to consult a local tax professional (in Canada) who is familiar with Canadian tax law and cross-border tax issues, including the tax treaty.
