BDUs are required by the CRTC to simsub *IF* the Candian signal is the same or higher resolution and the quality is justa s good. If the simsub feed is crap, BDUs do not have to carry it. If I were a Bell lawyer, I'd insist that the techs at the simsub centre tape both feeds, as documentation, just in case the CRTC demands to know why a show wasn't simsubbed.
Bell doesn't have to simsub a crummy signal over a good one, but they can. It's not that they feel such empathy about their customers' veiwing experience, but in most of the country, there are generally 2 satellite providers, a cable provider, possibly an IPTV provider, and maybe even OTA. If Bell gives customers a crummy feed, and a competitor gives a good clear feed, Bell loses customers; it's that simple. After the NFL playoff fiasco back in January, the issue is on the public radar.