Welcome to the community!
If you do not wish to travel using Fido Roam, you would need to contact customer service to opt-out of the service. Alternatively, you might consider sending @FidoSolutions a PM. Once they verify some information, they'll also be able to access your account. In addition, they can also be contacted via Live Chat, Facebook, or Twitter. Those methods can be accessed via the contact page posted above.
Once you are confirmed to have the service disabled on your account, your usage abroad would be on a pay-per-use basis. If you choose to travel without Fido Roam, you might consider disabling data and roaming data as those charges can add up quite quickly. You can view the pay-per-use rates here.
If you wished to disable roaming entirely, you would need to contact customer service and have them place a roaming block on your line. Alternatively, you might consider keeping your phone in Airplane or Flight mode. You could then manually enable Wifi when required. With Airplane mode enabled, the phone should not be able to connect to the local networks. You should note that if your phone is Wifi-calling enabled, some usage abroad would be considered roaming (see here). Another option would be to remove the SIM card from your device. However, if you choose this method, you would need to ensure you do not lose the SIM card. While you can order a new SIM, you would likely be charged for the replacement SIM.
Hope this helps 😀