Hello Bbailey15,
Welcome to the community!
Getting a local SIM card (or eSIM) is a method people use to avoid roaming charges. However, it does have its limitations for some people. The main issue is that the local SIM cards have phone numbers which are local to the destination. For some people, that is not an issue. However, it means that you will need to provide that new number to your contacts. In addition, calls to that number from Canada would be considered long-distance and incur additional charges for your contacts.
Generally, using a local SIM card means that you don't have to use your Fido services and avoids roaming. With eSIMs, you would need to ensure you know how your device works with regards to that functionality. If your device has dual-SIM functionality, selecting the local SIM may not entirely disable the Fido SIM and allow unintended usage.
That said, you note:
@bbailey15 wrote:
... use my Fido account while in the US for 5 months....
The Fido Roam charge incurs when your device uses Fido Services abroad. That is, the charge will incur when you make/receive calls, send text messages or use data outside of Canada (see here). With the exception of some Wifi-calling usage, using your Fido number outside of Canada is roaming and will incur roaming charges.
With regards to Wifi-calling, it should be noted that its usage is not free per se. I'm not sure how people have gotten the impression that Wifi-calling does not use the networks. However, that is not true. While the calls and messages do not transmit via cellular towers, they still use the networks via the internet gateway (see image here). The cellular towers and Wifi are merely alternate means of accessing the networks. Calls and messages would not be able to complete or get sent/received without the networks. As such, using Wifi-calling is technically using Fido services. However, they have allowed certain usage to be free from additional charges. All the messages and calls you receive (from anywhere in the world) will be taken from your plan's voice minutes and messaging limits. As well, all Wifi-calling messages and calls you make to a Canadian phone number while abroad won't incur long-distance or roaming charges (see link above).
Since your travels are in the US, you should note that the US have shut down their '3G' networks (see here and here). Customers need to have devices (and plans) which are compatible with voice-over-LTE (voLTE) capability.
You can certainly use a local SIM when travelling. However, doing so won't provide usage on your Fido account without roaming. If you wish to use your Fido account while in the US, that will incur roaming charges (unless specified Wifi-calling usage).
Hope this helps 😀
Cheers
