I am disappointed by this as well but they are fully in their rights. The issue came up with the decision by the CRTC to not allow Bell TV to have an alternate HD feed for last year's Super Bowl. The decision was wrong but we have to live with it until the CRTC is disbanded. I really don't see the benefit in this case as Sun TV doesn't sell a substantial amount of national advertising. Maybe with this new simsub they are intending in increasing this number. The Canadian station must request this simsub in writing several days before the event.
If you question this, you are within your rights to complain to the CRTC. Simply put your comments in writing on the CRTC website or by snail mail at CRTC, Ottawa, Ontario, K1A 0N2. In order for your complaint to be "heard" you must send a duplicate of your complaint to the licensee, in this case there are two, Bell TV and Sun TV, by registered mail and include the receipts from Canada Post which show the recipients. Unfortunately, the process is so bulky that most won't put in the effort to do it. To file on the website you MUST foillow the complaint rules as listed on the website to the letter. It is also highly advised that you also send copies of all corresondence to your local MP.
I support the process of simultaneous substitution if and only if it serves the purpose for which it is intended. That purpose is that the viewing public see commercials which are pertinent to their viewing area. In other words, the Canadian station which is being substituted must be showing a majority of commercials which are national in nature or apply to the viewers wherever they may be in Canada. It serves no purpose to inflict local Toronto (for example) commercials on viewers from Ft. McMurray, AB, or Sackville, NB. We don't have their local retailers so are never going to be doing business with them. So what difference is there in what location the program comes from, be it Vancouver or Boston? Only if the Canadian broadcaster is actually advertising to ALL the viewers in their simsub area should they be entitled to a simsub.
Also very important is that the substituted Canadian channel must be showing the exact same program starting and ending at the same time, the programming must be 94% identical to allow for commercial changes, and be technically equal or superior to the broadcast being replaced. This means that SD cannot replace HD and that if the US broadcast is shown in Dolby Digital then the Canadian one must also be. In the case of American Idol the producers use a modified Dolby Digital and the FOX stations on the network are not allowed to tamper with it. CTV did and, subsequently, lost their right to substitution until they "followed the rules". If you are in a position to hear both versions of a broadcast and actually hear a difference in the audio or see a difference in the video where the US version is superior you are in your rights to demand that the Canadian carrier drop the simsub. The carrier (Bell TV, Shaw, Rogers, etc.) is supposed to be monitoring all simsubs for technical quality.
This is a long winded answer but will hopefully answer a lot of questions and, ultimately, bring about more questioning of the Big 3 broadcasters and their oligopoly. They are the ones that need to be kept under wraps.