You say you are 'in Quebec five days a week for work.' But here you say you go back to Ontario unless you have a double shift.
Where do you go home, habitually, at the end of a normal shift? If you do a double shift, do you then have an extra day or two at home after sleeping and/or are double shifts not that common?
Look, I personally think this concern is exaggerated - which was the point of my joke about Anticosti Island, which is about 1200km from Ontario, BEFORE you get on a boat to the island. You can't commute to Anticosti.
The truth is that if you're registered as living in Ontario and not being outright fraudulent (i.e. spending close to zero time in Ontario and factually and obviously residing in a different province), no-one cares.
Going back to my questions: if you NORMALLY return to your place in Ontario at the end of a work day, you're probably fine. For people that do odd shift work and/or remote work where you reside at work or extremely long days (and hence usually also have more days off, like 4 on-6 off), it's mostly going to be where the majority of your time off/habitual residence is.
This is pretty much just common sense.
And again: mostly there is no-one checking. A car insurance company is probably going to pay zero attention UNLESS there's a claim and they incidentally discover and have an incentive to deny on basis claimed residence is clearly not truthful. (Likewise provincial health authorities, in principal - but same basic test of where the person seems to reside).
ALSO: despite comments and concern here that IRCC will be 'checking' cases where applicants seem to have moved before or during their spousal sponsorship applications, we actually have ZERO cases of actual evidence of someone caught up in this. (If anyone has any evidence, now is the time to share it)
Now, I'm not remotely claiming that anyone should lie, and applicants should assume that IRCC does NOT want to have issues with Quebec government, and common sense is that applicants also do not want to have IRCC officers deciding that they are misrepresenting their residence - or even suspicion of that. (If they think one part of an application is not truthful, they are probably going to decide other parts of the application are suspect, too - meaning likely delays while they check). I would personally suggest that those changing provincial residence DURING their application (after applying) should be a bit more diligent about providing evidence they've moved.
But let's not exaggerate. The fantasies of people on this forum who want to believe that IRCC is checking MUCH more carefully than there is any evidence of are mostly just that, fantasies. They don't have the resources and have better things to do.