I've also tried changing the region to Canada, on both iPhone and Watch, but I still see the same error loop.

Sadly the suggestions here have not fixed this for me. I have a brand new iPhone 12 mini, trying to pair with an Apple Watch Series 1. Hard reseting both iPhone and watch results in the same "Unable to check for update" error message loop. I have internet access, and have confirmed all the other sanity checks from the Watch support page. Can someone from Apple please escalate this case to the development team, pretty please! :) thanks