Hello CaptainBruce,
Welcome to the community!
Unfortunately, I don't think what you're trying to achieve is possible.
As far as I am aware, there is no text message (SMS/MMS) forwarding service from Fido (or any other provider). I do understand there may be some apps which are able to automtically forward messages. However, since those apps would be installed on the users' devices, the messages would need to be received on on those devices before they can be forwarded. Apple devices do have the ability to forward messages to other devices (see here). However, I believe the phone would also need to recieve the text messages first. If you are removing your Canadian SIM, your phone would not be able to recieve the text messages in order to forward them.
That said, the Fido Roam charges will only incur if your phone uses services -- make or receive a call, send a text message or use data abroad. It should be mentioned that while receiving SMS would not incur the roaming charge, any data contained within MMS (incoming or outgoing) would be considered roaming data and charged accordingly. You should note that MMS are not solely restricted to pictures or video messages. Messages with subject headers or group messages etc are also considered MMS. It should further be noted that iMessages and RCS messages are sent (and received) as data and not as text messages (SMS).
If you used the dual-functionality of your device, you could receive SMS on your Fido SIM without incurring roaming charges. However, forwarding those messages would incur those charges. You should note that some manufacturers might allow some data usage to occur despite data and roaming data settings being disabled (see here). You would need to know how your device behaves abroad.
Hope this helps 😀
Cheers
