for those who attended interview, is that standard that they ask for proof of cohabitation? Will they need only 1 document as a proof or we need to bring a few ? What is best proof to show?
Standard, no. But it happens and don't worry about that. If they would have real doubts about your cohabitation, you would not already have DM.
Possible proofs:
- lease or mortgage showing both names
- driving licence showing the same address
- governmental letters showing the same address (like notice of assessment from Canada revenue agency, letters from your province health insurance program,...)
- utility bills (electricity, internet, phone,...) showing the same address
- ...
One or many proofs? I'm always feeling better being on the safe side, so I would say bring many of them, but one (if they even look at it) should be enough.