SophiaSalah said:
But his legal status expired a few days ago. What worse could happen now? Is there no way I could sponsor him?
The CIC definition seems pretty clear about this, check the link below:
http://www.cic.gc.ca/english/information/applications/guides/5289ETOC.asp#who
Under the heading 'Sponsoring your spouse or common-law partner who lives with you in Canada' (about 1/5th of the way down the page). It says under the second bullet point 'have legal immigration status'. There is nothing about 'a few days here or there doesn't matter' and the one thing you can count on government departments around the world to do, it is to interpret the statements very literally. So I suggest it is binary, they either are or are not of a legal status - in your case I am afraid 'not'.
You can of course sponsor him via outland sponsorship if / when he returns to his country of origin. He would have to stay there until your application is properly lodged (ideally until Sponsor Approval), then he could perhaps try to come back to Canada under 'dual intent', but it is up to CBSA whether or not they would admit him under a visitors visa, which may be less likely if he has already overstayed.
I am not sure if you can apply for an extension to a visitors visa now (specifically what your chances are that it might be approved) and apply inland - others will be better placed to offer a view on this that me.
