57 is mostly right on what sim-subs are in the acronym list, except that Sim-subs replace the whole program with the Canadian station feeds. That matters, because on occasion (as witnessed in that other Sim-sub thread), the Simsub goes horribly wrong, often to to the process being largely automated.
Why Shaw Direct is preferred when it comes to Sim-Subs, is that they have the capablity to execute sim-subs at the customer receiver, and do exercise that capability by only switching customers obligated to get substituted, and with their local station.
Bell Sim-Subs all their customers at the uplink, regardless of their right to not be, and only by stations they decide, such as Toronto or Calgary.