Welcome to the community!
If you do not wish to use your services, your best option is to enable Airplane or Flight mode for the duration of your trip. Be sure to enable the setting before you leave Canada. You can then manually enable Wifi when required. Airplane or Flight mode will prevent your phone from connecting to the mobile networks. You should note that if your device is capable of Wifi-calling, certain usage will be considered roaming. Namely, using Wifi-calling to make calls and sending messages to non-Canadian phone numbers will incur the Fido Roam charge.
You might also consider contacting customer service to add a roaming block on your account. Alternatively, you could send @FidoSolutions a PM. Once they verify some information, they'll also be able to access your account.
Hope this helps 😀