They aren't going to be terminating individual PON connections onto backbones/trunks, the equipment is different and bandwidth on backhauls is reserved and paid for by the carriers/subscribers using it. Even our little semi-local ISP has their own dedicated fibre running from Millbook to Front St. in Toronto. Typically, the telco's follow the POTS routes for PON, and may opt to use the old DSL remotes as the termination points, where they then jump on whatever backhaul feeds the remote. Allows a lot of reuse of existing infrastructure, so it keeps the cost down. That's how Bell has managed their fibre deployment in Canada.
For Bell, maintaining 100+ year old POTS infrastructure has become more expensive than just replacing it with fibre, so yes, there may be financial incentives from the government to replace it with PON, but there's also the maintenance cost associated with legacy POTS, which they can eliminate when they replace it with fibre.