So follow-up on my setup (SIP/VOIP provider VOIP.ms; Softphone app Linphone):
I ended up going with VOIP.ms for the SIP provider (sorry @applesbana ). They are Canadian and have great chat service and detailed setup instructions and videos. Also from Montreal. Rates really good. Unfortunately KYC so I had to give them everything.
I have installed and failed with the following Softphone apps: Session Talk, ACR Phone and Bria Mobile apps.
ACR phone - calling worked fine; couldn't see any SMS functionality (my oversight),
Session Talk - calling worked fine; SMS didn't work properly - I would see the notification but couldn't access the SMS or send back.
Bria - couldn't get the app going because couldn't register with payment details as I downloaded anonymously in Aurora store.
I have managed to setup Linphone as my Softphone app. Push notifications working and I can receive/send calls and SMS so far.
I'll update again after I have been using if for a bit. Thanks to everyone who chipped in!