It is a real bummer as well that on a dual-SIM phone the Canadian version has that option removed. Why? Dare I say..."monopoly"?
legally, they have to test a device to make sure it's 100% compatible with their system.
so for example, if they don't test it extensively and your call to 911 fails because it's not compatible for some reason, you might end up suing them because 911 calls did not work. Also, regarding the laws, 911 calls shouldn't be blocked for any reason... so if a VoLTE fails for any reason for 911 calls, they might be in trouble.
so essentially here, Videotron has probably asked Huawei to not enable VoLTE when an Videtron sim is inserted because it's still not fully tested with their system.
@zadigre This should teach me to be more explicit...I was just talking about the dual-SIM option disabled on the LYA-L0C (Canadian) version of the Mate 20 Pro. It wasn't a continuation of the discussion about VoLTE.
Hence the comment about monopolies in Canada and the push back on diual-SIM phones.
Hope I clarified things now.
BTW...for those interested - once the bootloader is unlocked (not trivial or free today) there is a chance to flash a LYA-L29 ROM and get dual-SIM functionality...or so I read.