Thanks for a great Trip Report, Matt_01. I really enjoyed seeing and hearing about your experiences in Harbin and Sapporo, at what appears to be the full depth of winter in each. We have been to both on separate trips in the past couple of years, including Sapporo in December 2019 and Harbin in February 2017. Neither place was as cold and snowy as you experienced, but still pretty cold for a couple of Queenslanders.
We stayed at the Sofitel in Harbin, and I would thoroughly recommend it. A great Executive Lounge and wonderful service. We took the overnight sleeper trains (first class) from Beijing to Harbin and return, which was OK as trains go, but not very comfortable. The Mercure in Sapporo was good, and we thought Sapporo was a very welcoming and modern city.