Starting in 1883, CPR began using the O&Q to build a network in southern Ontario to compete with the Grand Trunk Railway.
In August 1888 they provided a direct through route to Montreal by leasing the Atlantic and North-west Railway and connecting it to the O&Q via an extension from Smiths Falls to the Quebec border.
A final major extension was the West Ontario Pacific Railway (WORP), which connected the Credit Valley in Woodstock to Windsor and the US border.
The CPR never owned all of O&Q, a fact that caused legal problems when it attempted to sell off some O&Q real estate in Toronto that had become quite lucrative.
[8] While O&Q and the TG&B had always been operated as part of the CPR network, they were finally amalgamated to form the St. Lawrence and Hudson Railway in 1998,[9][10] as a consequence of a corporate reorganization undertaken by CP.