LOL 13-16 hours in a civic with a Great Dane! Good luck.
Just remember that Dec/Jan is cold, so if you're planning on outdoor stuff, you might be relegated to snowshoeing, ice skating or skiing. Right now is great hiking weather, but snow usually flies at any time now (none yet). Last year was a fluke and I think you probably had more snow in PA/NJ/MD than we did up here, but that's not normal.
Rockland/Rockport/Camden/Belfast (and all of 'mid-coast') are very accessible, have great shops/restaurants, and pet friendly (I lived in Rockland for a year and had 2 G.Shep dogs). Camden is a little more upscale, but has the mountain right there for hiking/snowshoeing/etc. You tend to get a lot of bang for your buck there because there are hilly/mountain coast, working towns/villages, good food/shops, etc. and aren't "seasonal" like the southern sand beaches.
You missed the Lobster and Blues festivals (Rockland)-- they're summer events. There's always the ferry to Vinalhaven.
Of course Acadia (Bar Harbor) is the gem with Cadilac Mtn and the national park.
Inland winter destinations are Sugarloaf or Sunday River (ski mountains).
Here's some webcams:
Portland is the 'big town' (largest city, 60k people). The "old port" section is easy to get around, too.
If you drink beer, then Allagash, Geary's, Shipyard, and Sea Dog are the most well known local micros. Cold River vodka is made here from Maine potatoes
The whole state is a big park, so it can be overwhelming. We've been up here over a decade and still haven't hit all the destinations.
Hope this helps. Have fun!