Using the former CP Belleville Sub (aka the Don Branch) assumes that ML would reactivate the old CN Leaside Spur which ran from the Bala Sub at Oriole down to CP at Leaside.
While some might argue that it was "railbanked", I am confident that there would be intense pushback if the idea of restoring a rail line along that corridor were put forward..... partly from residents along the trackage, and even more from people who have come to see that as part of the city's trail network.
I am willing to bet a steak dinner that it will never, ever be repurposed as a transit line. Be sure to call me to collect if it happens, but in the meanwhile - I really think this has become a fantasy idea and is no longer a serious transit option, even if it makes eminent sense..
- Paul