Correct, though I’m not sure if you can send or receive RCS messages in airplane mode. If not, you might want to consider something like WhatsApp or another chat messenger that uses WiFi, not cellular data. That way you could even remove your Canadian SIM during your travels and use a local one instead, to have Internet on the go.
To clarify even Sending back text messages will trigger easy roam.
If you have your RCS settings set to send as SMS if RCS fails, then any outgoing text messages that go through will trigger easy roam.
I would personally turn off data and data roaming settings in your phone. Then I would turn on airplane mode and turn on wifi and then take out my sim card. If for some reason I needed an incoming text (2FA, etc) I would then pop in my sim card.