Yeah, but that's an immigration issue, we're talking about taxes. Under US and Canadian law if you're married you have to file jointly, the CRA and the IRS don't give a damn what your immigration status is, you could be in the country illegally for all they care. In addition a spouse is a "residential tie" to that country. If he hasn't claimed permanent residence in Canada then they can choose either the US or Canada, but if he does get LPR status in Canada then it will definitely be Canada because a claim of permanent residence is exactly that. Whether it's abandoned or not later on is not really that important, the calculation of where your tax home is in this situation is somewhat murky, so the fact that he wants to permanently reside in Canada whether he meets the letter of the immigration law or not is what counts - and he showed that by getting LPR status to begin with.
Without him ever having LPR status it gets more murky, depends on the amount of time he spends in either country, how long she spends in either country, etc. There is a formula for calculating it in the tax treaty but also you need to check the case law on it.
Certainly if they choose the US, the CRA aren't going to be happy about a Canadian resident family filing as non-resident ad infinitum, which is why she needs a lawyer really because when they ask her to fill in NR-73 she needs something to back it up.
To be honest the simplest way out of it is to not be married, or live in the same country!





