Principally residing is not enough. You can have a primary residence in Canada while spending months out of Canada. The requirement is that you must remain in Canada if a PR to sponsor a spouse not have a primary residence
You're correct in that I didn't intend 'principal residence' here in any technical sense - such as CRA usage; I meant only actually residing most of the time.
But then I didn't think anyone would seriously use 'commuting from Canada' in quite so broad a sense, either.
So @Murchan - I wouldn't suggest playing with terminology with ircc or cbsa officers. They're going to think that residing in Canada and commuting means most nights and weekends in Canada. You seem to be using it in a way that might mean, ummm, a couple nights a week? They'll have your info - including crossings - and are not so stupid as some seem to think.
And no, just removing yourself from the flat you share with your spouse is probably not going to be convincing.
That said, no idea how much ircc is likely to pay attention to this.