"CTC" may be a bit extravagant, although it is referred to as such in ONR employee timetables. To be more accurate, the diamond between ONR and CN at Dykstra was an interlocking plant controlled by the CN Operator at North Bay, who also had control of some switches, with associated signals in the zone between it and the CN station. The jurisdiction over tracks between these points was split between ONR and CN, with the closest track to the depot being an ONR track (but used at times by CN passenger trains to make their station stops).
Some tracks around North Bay had ABS signals which would have been affected by the interlocking as well.
You are correct that CTC on the Newmarket Sub ended at Gravenhurst, this was cut back to Washago a decade or so ago.
- Paul