You won't get any discount unless you cancel. Shaw is very different from Bell or Rogers, you only get deals after you actually cancel the service. They will call you back in a week or so, it will be a different department that can you give you some discounts to try and convince you to come back. I got about $30 off my bill for a year, and 2 free HD Recievers (non-PVR model). Sadly the discount is only for a year, but the receivers are free. After a year, repeat the process (it's no contract). I didn't even unhook my receivers, they were just out for a week.
It's actually very easy, but like I said, unlike Bell or Rogers, with Shaw they will always call your bluff. You must cancel first, then they try to win you back.
You can tailor the deal to your liking as well. If you don't need new receivers, go for a bigger monthly discount (ask for about $40 off).
Also, never except lower programming bundles. They have a certain dscount cap they can work within, and will try to use as little of it as possible (I heard it's about $300 to $400, but I can't confirm that). I would advise asking for free hardware (if you need it), and going for a higher bundle with a larger discount, or the same bundle you had before, with a much larger discount.
By the way, keep in mind you can reject the deal. They will call you back a second time I believe.
“My biggest problem with modernity may lie in the growing separation of the ethical and the legal.”
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-Nassim Nicholas Taleb