A historic route on the Canadian Pacific Railroad, famous for the horiffic disaster in 2013, the line between Lac-Mégantic and Sherbrooke is well known among locals. The line runs for roughly 90-100 kilometres through Canadian countryside along well used rails, well known among all kinds of people. A line rich with history, and incredible heavy freight traffic, this line would suit TSW3 well. The Rolling stock the line could use can vary, depending on the era. Pre 2013 the line could run with BN liveried C30-7 and B23-7s, under the MMA railway. However, because of the aforementioned train accident in 2013, the company went completely bankrupt and got shut down, before CP rail took over. I think that the AC4400cw, SD70ace or the ES44AC suit this line very well, as well as the SD30C-ECo or the GP38-2 could fit this line very well. Below is aink attached to a video of a train at Lac-Mégantic passing by.
I suspect this could be too hot for DTG to touch precisely because of the accident. It's also a relatively unknown route otherwise so might not be commercially viable.