For services that connect the various cities, yes,build it and they will come. However, the Sudbury- White River train is not that. Were it to be extended to Thunder Bay, then, less marketing would be needed. An example, the Northlander likely won't need much marketing to make it viable as it connects enough people along it to become viable if people know it exists. The Northlander is more like a Corridor train in that regard. The Sudbury - White River train does not connect enough people to make it viable just on those trips alone. However, there are enough people in the area/province/country/world that if it were marketed as a way to see nature that it could be filled. Though I haven't yet taken the 2 routes in Quebec, and the Gaspe train, I suspect these routes also could be marketed much the same way.
I have not changed my tune though, as I don't think I have ever suggesting adding services that do not connect a reasonable number of people. I am looking at these routes and asking how they can be made viable. That is the question the marketing department of Via should be asking, and then should be implementing.