just do a search on the China forum, this comes up all the time.
Don't bother booking way in advance your intra-China tickets. Generally speaking the discounts to standard fare are zero or minimal and then the discount starts to improve as you get closer to the date. Then, a day or two before the flight, the fares usually go back to zero discount. The discount you can get varies but I've had up to 70% off, 30-40% is common
I think I am correct in saying that overseas travel agents cannot access the discounts, they will only sell full price fares (I had this when I started travelling to China and quickly started to book them myself)
two good websites, both of which you can book from outside China with a Credit Card. I've used them loads of times. At the very least they will show you the discounted fares and you can then check that your Canadian travel agent is getting the same prices
http://english.ctrip.com/
http://www.chinaticketmaster.com
nickyboy