Airtunes does not need an internet connection so the speed of the Telus stick shouldn't matter.
I am guessing that since you are sharing the Telus internet via the Airport card in your Macbook, it over rides the Airport connection to the AP Express.
As a test, try disabling the internet sharing on the Macbook. Have the Telus stick for your internet connection and connect to the AP Express. You may need to set your service order in System Prefs to put the Telus stick as first priority.
Once connected to the AP Express, iTunes should be able to see it for Airtunes even though the Telus stick is providing internet access.
If this works, that is great for 1 computer. Your second computer will be out of luck unless you can wire them together and share the Telus internet that way. That would require some tweaking I'd bet