I have a client who married a Canadian citizen in Canada, and had moved to Canada in October 2023.  How should I file his return - I don't want to do single, since he is married.  I don't think I should do married filing joint because the spouse never lived in the US, and none of her income was earned here.  Since she is not required to file a return here, I considered filing married filing separate.  However Canada uses an SIN which is similar to an SSN in the US.  Since MFJ or MFS will require me to identify the spouse, can I use her Canadian SIN on the 1040 instead of an SSN which she doesn't have?  I'm afraid it will bounce back because the number will not agree with SSA.

I would greatly appreciate any advice anyone has for me on how to handle this situation.

Thank you.