You've plenty of time then.
Essentially you'll probably want one of three options for crossing the channel
1, short crossing via Dover
2, tunnel
3, I would favour Dieppe / Newhaven
Many other crossings are available, depends what you want. You could continue driving to Holland and get a crossing to Hull.
As you will be in a motorhome you can take your time and ensure enough time for adequate stops for your dog. There are thousands of options for places to stay overnight.
Consider how your dog will deal with the confinement of the crossing. It might be only a few hours that he will be locked in your van on his own.
Research the crossings and what they provide. If I can help further let me know