According to the live Stena Line freight timetables the Cherbourg sailings of the STENA HORIZON appear to be cancelled from 1st of January and she appears to be operating on the Birkenhead - Belfast route. Presumably whilst the vessels on there are dry docked?
The only "cancellations" I've seen over the past 2 days on the route are what I'd normally expect to see over the Xmas and New Year period. The problem of course with the live timetable is just that - it's live! If something is being changed on it then thats what you see, even if it's only temporary while something else is being changed. At present Horizon is showing as being on her own route and the Birkenhead route at the same time, with Lagan being the other vessel on the Birkenhead run for the entirety of January! Thats obviously not going to be the case if both vessels are to be dry docked this year, which I believe they are.
It has been normal practice in recent years for Horizon to cover Birkenhead though, while the relief vessel covers the France route (Flavia or Nordica in recent years). Still no public announcement as to the relief vessel but I'd be surprised if it isn't Nordica tbh. I'm sure something public will appear in the coming days or weeks anyway, given we are talking 3 weeks away now. Perhaps they are delaying the "announcement" for operational or commercial reasons?
Edit: by something public I don’t necessarily mean any specific announcement or press release, more likely the name of the vessel on the timetable will simply change or a different vessel will just appear! Bookings are still being taken so there’s definitely something running