It appears that chromecasts are not working on my TELUS network primarily due to multiple access point and possibly the multiple wi-fi bands being "AP Isolated". This means that when you want to see a chomecast on the the network from your phone it is only working if they both happen to be connected to the same access point (either the router/gateway or an extender).
I've logged into Arcadyan admin console and chatted with someone on the fiber network support team. It sounds like AP Isolation and even band steering are not configurable on a TELUS Arcadyan router network.
I'll be returning my 2 TELUS Boost Wi-Fi extenders, and setting the Arcadyan to bridge mode (which you can) and then purchasing my own more full featured mesh network router and hardware. I also mentioned to their the tech that they should warn people about this because they do currently promote and even sell chromecasts. Their wireless mesh LAN seems more like it is just a wireless mesh internet access point. This is disappointing as there are other home automation products with will be impacted by this fundamental limitation.
Hope this is helpful to someone.
I got my 2.4ghz only smartbulbs set up on the Arcadyan wifi hub by enabling Wi-Fi > Smart Device Network. It creates an unbroadcasted 2.4ghz network so you could manually connect your phone/other set-up device to that and set up anything that requires a 2.4ghz network that way. It's been working fine for my bulbs.