1. Pay them - my logic has always been this, they need a deposit for the next place, they need an upfront payment, if they are so chaotic as to be in arrears they won't have this money so you have to 'help' them to leave. I had to do this once, and it was the best money I ever spent.
Cash on day of leaving when bags are packed and outside. Take pictures and a witness. Do everything by the book.
2. The heavies. I don't recommend this, it's illegal and you'll end up in big trouble.
3. Illegally evict them. You've done everything right, they are in arrears, PRTB as this landlord has found out is absolutely toothless and is leaving the landlord, who is paying for the PRTB to sort out the mess. BUT you risk the PRTB fining you big time. I think the worst I saw was 20K.
What I do not know is would the PRTB in a case where they have given a dertmination order against a tenant to leave, and a tenant in arrears to boot, would the PRTB have the neck to levy a large fine in such a case. I think not but I'd research this before proceeding.
Note: I have no issue with PRTB issuing large fines to landlords who illegally evict etc as long as the landlord has gone through the proper procedures with the PRTB and I'm totally against the unfair situation a landlord finds themselves in after wasting a year or so with PRTB procedures to find out they now have to spend another year or so in court - as the PRTB well knows.
4. Go after the PRTB to enforce the eviction by going to court. PRTB have money for this but they don't want to spend it on lawyers and they have classified this area of their work as a low priority.