An Audi A6 Allroad might be a good choice. There's a new model on its way, but that means there are some excellent pre-registered deals on the outgoing model. You can pick up an as-new example with delivery miles for less than £36,000. It's got a big boot and access for a big dog will be easier than an SUV. It's also fairly capable off road and a set of winter tyres would make it unstoppable in the snow. Alternatively, consider a Skoda Kodiaq with a ramp to get the dog in the boot.