Try turning Smart Steering off if you have it on. It might be the devices flip-flopping between the 2.4 and 5 GHz WiFi. With Smart Steering off it forces the devices to stay on whatever WiFi you set it up on.
To turn off Smart Steering - do this:
1. Make sure you are on the Telus wifi on your laptop/ipad.
2. After connecting to the router, open a browser and go to: http://192.168.1.254
3. Login with the user ID that's on the label on the T3200 Router (and not the extender). This will be different than your wireless access code.
4. click on "Wireless Setup"
5. Disable Smart Steering and try again
Btw, i had similar issue with my original generation Chromecast as well. I never did disable Smart Steering as I didn't know about the option back then.
I solved it in two ways:
1. I hard wired the Chromecast. Bought the Chromecast Ethernet Cable on Amazon ("Cable Matters Fire Stick Ethernet Adapter") for 20 dollars. All streaming problems on Chromecast went away.
2. I was still having Wifi issues in general and got a Google Nest Wifi to bypass the T3200 modem. The Google nest was fine for Chromecast, but now you have two separate networks.