Pointing out the obvious, in case you haven’t seen it.
https://www.poferries.com/en/routes/dover-to-calais/travel-information/travelling-with-a-pet
Apart from that, we sadly don’t have a dog (yet), so.. Only thing i can say is that you may need to be careful in germany depending on the breed of dog.
Germany has Pitbulls, Staffords and Bull Terriers banned – that includes transit. Now there are exceptions for service dogs, but that requires extensive documentation.
Assuming that we’re talking about one of them, anyway – you didn’t specify, just wanted to point that out.
Prior: SEAT Ateca Xcellence Lux 1.5 TSI DSG MY19, VW Golf GTE PHEV DSG MY23
Current: Hyundai Ioniq 6 Ultimate
Next: we'll see what's available in 2028.