Welcome to the community!
Sorry to hear you're having issues with cellular reception in your area. There appears to be a few Fido/Rogers cellular towers in those areas:
~taken from here.
Coverage would depend, in part, on your location relative to those cellular towers. I understand you might not have had issues with your previous provider, however, that would likely be due to your location relative to their cellular towers.
In addition to proximity to cellular towers, there are many factors which can influence cellular reception (see here and here). There could be more interference between your location(s) and Fido/Rogers cellular towers versus the other providers' towers.
Furthermore, different mobile devices can vary in their cellular receptivity. That's why no mobile provider can guarantee service. There are just too many factors beyond their control. Also, what phone are you using? Was it purchased from Fido? If it was purchased from elsewhere, have you verified it has the necessary compatible bands/frequencies? You can view the compatible bands/frequencies here.
It's possible your device may connect to the other providers' cellular tower as extended coverage (Fido-EXT). With the roaming agreements, there is no charge for using extended coverage. However, there are some limitations to its usage (ie majority of your usage still needs to be your home network).
If the Fido/Rogers cellular signal is not adequate in your area (or your device is unable to receive the available signal) , you might consider purchasing a signal booster. If you choose this route, you would need to verify the product amplifies compatible bands/frequencies.
Unfortunately, if your circumstances don't allow for adequate Fido/Rogers cellular signal, there isn't much that can be done. It's a common misunderstanding that any mobile provider will suit everyone everywhere. That simply isn't the case. If you spend a good portion of time outside of a mobile provider's coverage, perhaps that mobile provider isn't the right one for you. As previously mentioned, the majority of your usage needs to be on your home network. If you live outside of (or on the edge of) Fido/Rogers coverage, you would likely need to switch the network providing the extended coverage.
Alternatively, if you have access to Wifi and your device is supported for Wifi-calling, you might be able to continue with Fido using that feature while you're in those areas.
Hope this helps 😀