Using your device to make a WiFi call or send a text to a non-Canadian number while travelling will incur roaming charges, such as the Roam Like Home daily fee.
If the number you’re calling or texting is outside the destination you’re roaming in, you’ll also incur long distance charges.
When using WiFi Calling, you won’t be charged for incoming calls or calls back to Canadian numbers, including checking your voicemail. "
There may be other similar instances, but that's all I found for now. So Airplane Mode is no guarantee if you utilize other phone plan features...
I cannot speak to the issue of Hot Spots.