So I just signed up with Fido, and brought my own Google Pixel 2 XL which I purchased directly from Google Store. I saw the option in my phone settings to turn on WiFi Calling. However when I went to slide this toggle on, I got a message saying that my device wasn't compatible with this feature. I searched through Fido Support and the community forums and realized that only Fido purchased Pixel 2's will work with VoLTE and WiFi Calling. I also noticed that it says non-Fido purchased iPhones may work with these features.
My girlfriend has an iPhone X (not on the Fido network), so I just decided to take a shot in the dark and put my Fido Sim card into her iPhone to at least see if I could register for WiFi calling on my account. When my Fido Sim Card was in my Girlfriend's iPhone X, I toggled the WiFi calling option and successfully registered WiFi calling on my Fido account and it had me input my e911 address location. I then took my sim card out of the iPhone and placed it back into my Pixel 2, went back to toggle the WiFi calling option, and voila, it said WiFi Calling was now working.
I also tested making a call while not connected to WiFi to see if my connection remained on LTE in order to verify VoLTE status, and while the call was in progress, my connection stayed at LTE+. So it appears that a workaround for non-Fido purchased Pixel 2's and 2 XL's is to find a friend or anyone you know with an unlocked iPhone to borrow and put you Fido sim card in there and proceed with setting up WiFi calling on that device. Worked perfectly for me. Hope this helps other in the same boat.