Mackenzie and Mann began their first significant expansion outside of the prairies with the purchase of Great Lakes steamships, the fr:Quebec and Lake St-John Railway (1906) into northern Quebec's Saguenay region and the acquisition of branchlines in southwestern Nova Scotia (the Halifax and Southwestern Railway) and western Cape Breton Island.
Other acquisitions were in southern Ontario and a connecting line was built from Toronto to Parry Sound.

In 1908, a line, which under later CN ownership was known as the Alderdale Subdivision, was built east from a connection at Capreol, Ontario, on the Toronto – Parry Sound line to Ottawa and on to Montreal.
In 1910 a direct Toronto–Montreal line was built.
In 1911, federal funding enabled construction of the line Montreal – Ottawa – Capreol – Port Arthur.
In 1912, with GTR and CPR holding the ideal southern routes around Mount Royal to downtown Montreal, CNoR started building a double-tracked mainline north by excavating the Mount Royal Tunnel.
Mackenzie and Mann began their first significant expansion outside of the prairies with the purchase of Great Lakes steamships, the fr:Quebec and Lake St-John Railway (1906) into northern Quebec's Saguenay region and the acquisition of branchlines in southwestern Nova Scotia (the Halifax and Southwestern Railway) and western Cape Breton Island. Other acquisitions were in southern Ontario and a connecting line was built from Toronto to Parry Sound.
In 1908, a line, which under later CN ownership was known as the Alderdale Subdivision, was built east from a connection at Capreol, Ontario, on the Toronto – Parry Sound line to Ottawa and on to Montreal. In 1910 a direct Toronto–Montreal line was built. In 1911, federal funding enabled construction of the line Montreal – Ottawa – Capreol – Port Arthur. In 1912, with GTR and CPR holding the ideal southern routes around Mount Royal to downtown Montreal, CNoR started building a double-tracked mainline north by excavating the Mount Royal Tunnel.
Canadian Northern Railway