The CPR formalized its association with the O&Q by obtaining a 999 year lease on it in 1884. This lease expires in 2883. By 1890, this lease gave the CPR an extensive network in Ontario and Quebec, with lines reaching between Quebec City and Windsor, Ontario, as well as a line running from near Ottawa to a connection with the CPR at Mattawa, Ontario.
The CPR never owned all of the 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. However, the CPR won the court battle.
While the Ontario & Quebec and the Toronto Grey & Bruce railways existed on paper until 1998, when they were merged into the St. Lawrence and Hudson Railway, they had always been operated as part of the CPR network.