Don't look on Mount Desert Island
I've been visiting Acadia for ten years now and my in-laws are locals. It is very unlikely that you would find a moose on Mount Desert Island, where Acadia National Park sits. They get a moose sighting maybe once a year on the island so if you do see one there, consider yourself really fortunate. Coming in from Bangor, you aren't likely to have much luck along that route either but who knows. If you take a slight detour and take 180 past Graham Lake towards Ellsworth you'll increase your chances a bit from taking the normal roads. If you have the time, towards Baxter State Park is your best bet but that's headed entirely in the other direction. Happy moose hunting and enjoy the summit.