It can be approved with less than 6 months. Mostly affects your visa expiry. Your visa expiry will just be earlier than your medicals.
I'll suggest you go ahead with the renewal process pending when you get PPR. Then raise a CSE and submit the new passport with a copy of the old's bio data page for visa & COPR
Okay, thank you Tobs. I would start the processing ASAP to avoid unnecessary wait especially with a VO like Montreal that may send ADRs and after submission of ADRs may not pick the file up again till God knows when