(FRI) Canadian National filed with the U.S. Surface Transportation Board a plan to combine three of its U.S. rail subsidiaries into one.Under the plan, CN would fold its Duluth, Winnipeg & Pacific and its Duluth, Missabe & Iron Range operations into its Wisconsin Central operations, which it said would enable crews from these railroads to run over any of the three.CN said that, following favorable advice from the STB, it would then work to negotiate new agreements with the unions representing these railroads train and engine personnel. (ffd: Trains)