There are a few access points for Acadia National Park in the winter! According the Acadia National Park Services website –
Although most of Park Loop Road is closed in winter, two sections remain open, Ocean Drive and Jordan Pond Road. Scenic areas of Acadia are also visible and accessible from public roads that travel through and along the park.
Ocean Drive: scenic, one-way portion of Park Loop Road is accessible from Schooner Head Road, one-mile (1.6 km) south of downtown Bar Harbor on Route 3, and stretches for 2 miles (3.2 km) along the coast. Stay in the right lane, as snowmobiles are permitted to use the unplowed left lane. Exit Ocean Drive via Otter Cliff Road to Route 3.
Jordan Pond Road: two-way and accessible just north of Seal Harbor. Follow the Jordan Pond Road to Park Loop Road, which is plowed to the Jordon Pond House Restaurant parking areas.
Sargeant Drive to Northeast Harbor and Route 102A to Bass Harbor Head Lighthouse also offer scenic winter views of Acadia and Mount Desert Island.