There is a power of attorney form. I used it which allows you to do a TM30 if your landlord can’t or won’t do it. As everything is, it is dependent on what province you are in.
Just a note, the last time I got my marriage extension the 30 day under consideration period actually ended up being about 50 days. I made sure my funds stayed above the 400k threshold until I got the renewal. Immigration did not ask to see another print out to confirm my funds, but I have seen posts of guys stating they were asked to show proof of funds again as their under consideration period had been extended as well.
I know what the proxy form is. I am asking has anyone ever had to do one? I'm just doing diligence before I submit my TM30 when I move. My research shows it is rarely asked for.