I will tell you how our case was treated since there are many similarities
Interview in Montreal
We were both living in Canada at the time, but had a house purchased in US where we intended to establish domicile. During the application and interview, we made it clear that our newly-purchased, empty, US house was considered our domicile.
We were also clear that the US spouse was temporarily in Canada with the Canadian spouse, but both of us were intending to re-establish domicile in the US at the same time (there is no need for the US spouse to move beforehand). Similar wording was included as a note on the application. This was in no way a hindrance for our application. (I think your lawyer may need some schooling.)
We were required to have a US bank account with a high enough balance to cover 3x the federal poverty level. (Money in Canada didn't count.) However, this in itself was not considered sufficient support by the interviewing officer even though technically it should have sufficed. We were required to have a co-sponsor.
I had a letter from my Canadian employer that my employment could continue when I lived in the US. The interviewing officer completely disallowed this income from consideration. If the income wasn't on a US tax return from a US source, it didn't count. (I understand this could be handled differently by different officers)
I tried to get a US drivers license, but some (maybe all?) states don't allow that until you are actually residing in the state. Having a "domicile" for immigration purposes was not sufficient to get a drivers license.
I had communicated with a school about enrollment, even thought we never intended to send our children there. That communication was useful, as it was mentioned by the officer at the interview as proof of intended re-establishment of domicile in the US.
Keep in mind that this is a family re-unification visa. You do not have to tear the family apart to prove that you want to be reunited. Just make sure that you are clear on two points: 1) where is your domicile (US), and 2) you intend to re-establish domicile together.