Please Tony, would you mind posting with your Capitals Lock Key in the OFF position. I find it very hard to read as it is. Many thanks.
As regards 'pets welcome', might I ask what type of accommodation you are looking for? If it's a flat, holiday home or a house, and you know whereabouts (roughly!) in northern France you'd like to be, might I suggest you contact the local tourist office or departmental tourist board for their HEBERGEMENT listings - accommodation - which should cover 'gites, appartements et maisons'. There are usually symbols to indicate whether pets are permitted.
However, there are regulations in some areas of France as to whether dogs are allowed on public beaches and at what times. Again I'd contact the local tourist board for information.
I presume that your dog(s) are chipped and have their pet passport ....
I hope that puts you on the right track. Please post again with further information if you feel that HT could help you further. In the meantime, have you considered looking at
INVALID URL which although it is for owners, might lead you to properties which suit your requirements ... and they have a forum on which you can post once you register ...