Hello Lancet11,
Welcome to the community!
The main consideration with the '3G' network sunset would be that all devices would need to be capable of voice-over-LTE (voLTE). Once the WCDMA/UMTS ('3G') network is decommissioned, voice calls and text messages will no longer be able to fall-back to that network. Calls and messages will have to transmit via LTE.
I understand people are concerned about losing the '3G' network and Fido customers not being able to access the 5G network. However, other than devices needing to be compatible with voLTE, I don't think people will notice any change in service. With regards to coverage, I don't expect any noticeable changes. The band/frequency currently in use on the '3G' network will likely get re-farmed to the LTE network. So any loss in the '3G' network would be a gain on LTE.
I also understand some people are concerned about the capacity of the LTE network. There is often a comparison of the 5G roll-out to that of the LTE network. However, there is a difference between the two situations. At the time, the WCDMA (UMTS) or '3G' network was handling most of the call and some data traffic on only one or two frequencies for all of Rogers branded customers. Even if all Rogers customers used LTE for data, all their calls would still have been routed through the '3G' network because voLTE hadn't been introduced yet (announced 2015; see here). All Rogers calls & all of Fido's data and calls & all of Chatr's data and calls & all of the other MNVO data and calls would have made the '3G' network practically unusable, even for calls. Opening Fido customers up to LTE at that time freed some of that burden on the '3G' network. The situation is different now as LTE is much more capable than WCDMA/UMTS. Not only is LTE technologically more capable than '3G', there are currently many more bands/frequencies in use (see here). The decommissioning of the '3G' network would only add to that capacity.
Hope this helps 😀
Cheers
