I happen to have Bell Sympatico High-Speed, and I always take 15 minutes to do a little research before calling every June when my one-year contract from the previous year is almost up.
Armed with a rival (usually TekSavvy)'s rate for the same level of service being much cheaper, and knowing full well I'm more than willing to switch if denied some sort of deal, I call up and tell them that if they can't match the other (i.e. TekSavvy)'s offer I will switch at the end of the contract.
I have always gotten a price match + more for a new 1 year contract. This year was a jackpot; without even starting to negotiate anything they flat out offerered me the new customer only signup terms (3 free months, 3 months @ $20, 6 months @ $30).... great success.
Now, if I were to have called and said "hey give me the new customer only deal" they would have refused. It's all about leverage, and willingness to switch if you find a better offer. In your specific case, if you're telling them that for Package A of channels you can go to Rogers/Starchoice and get it for cheaper, they will negotiate. If you say you'll cancel and get whatever you can get for free, I doubt they'll even try to retain you (that would be like me calling Sympatico and threatening to go to dialup and then asking for a price match/discount on High Speed)
If you can't find a lower price, then why would they continually offer you lower prices than what everyone else pays? At least in my case, I can get the exact same service for cheaper than the normal Sympatico rate if I switch. If your threat to switch carries no gravitas, this severely hampers your negotiating position.