Reddit reviews The Expanse - Season 1 (4K UHD)

Amazon will stream it internationally simultaneously. They've also just added the first two seasons in Ultra HD 4K to the US service, which is great.

https://www.amazon.com/Expanse-Season-Ultra-HD/dp/B01MT0UHLT

The question will be what happens to Season 3. That depends if Amazon buy out Netflix's deal and move the first two seasons to Amazon Prime and can then show Season 3 immediately, or if they simply take over the deal, so Seasons 1-2 will remain on Netflix, Season 3 will air in the autumn and then Season 4 will be on Amazon. Those details haven't been announced yet.

Here it is at Amazon in UHD: https://www.amazon.com/gp/video/detail/B01MT0UHLT/ref=atv_wtlp_wtl_0

The dropdown lets you get to season 2.

Season 3 isn't available yet in UHD, as far as I know.

I find it easiest to add stuff to the Amazon watchlist from the website. That way, you can just go to your watchlist once you're in your smart TV/Blu-ray player/streaming device's Amazon app.

I'm not sure about Canada, but in the US the 4K UHD releases are on a separate video page on amazon. Here's the links that work for me, maybe they work for you too?

Season 1 UHD - https://www.amazon.com/dp/B01MT0UHLT
Season 2 UHD - https://www.amazon.com/dp/B079PB9KFP
Season 3 UHD - https://www.amazon.com/dp/B07GL8W69N