If you buy the phone from Fido then yes it will work with all of Fido's Voice and Data plans and features like VoLTE and WiFi calling depending those features are supported by the model of phone you get.
If you are not getting the phone directly from Fido then you need to make sure the phone has the compatible Band/Frequencies required to operate on the Fido network. See this post here for the required Band/Frequencies the phone should have.
If the phone was not purchased from Fido but it is a phone they carry then you can get features like VoLTE and WiFi calling to work depending the phone have the features.
Fido started allowing those features on non-Fido phones starting from the Galaxy S8 and newer.