Hi
Apple Watch (GPS + Cellular) is not locked to any specific carrier and has a built-in eSIM that copies information from the iPhone's SIM card.
The built-in cellular features require a carrier plan in your country of use that specifically includes support for Apple Watch (including the carrier activating the device on the plan).
I suggest that you contact Rogers to ask about their plans for offering service plans for iPhone that include support for Apple Watch Series 3 (GPS + Cellular), including model compatibility.
If you do not wish to sign up with a supported carrier for now, then you cannot currently use the built-in cellular feature.
However, Apple Watch Series 3 (GPS + Cellular) can still be paired, set up and used for other features whilst skipping the steps to activate cellular. The cellular feature can then be enabled later, if and when you are using a compatible service plan on your iPhone.