My wife and I are planning to travel to Maine for about 7 days after Labor Day weekend. I have not looked at flight options from Florida but may fly into Boston and drive to Maine. If whales are still in the area we would like to go on a whale watching cruise. My question is - is Bar Harbor/Arcadia National Park a must see or are there other areas/towns which may be closer to southern Maine that are worth visiting. We have never been there. We also like moderate hiking (not strenuous climbing) and biking as a daily activity (for a few hours at most) and eating lobster rolls.

Thank you for your suggestions.

If you do fly into Boston, I suggest that you take one of the Amtrak Downeaster trains to either Portland or Freeport. The Freeport Amtrak station is within walking distance of the LL Bean flagship store.
Rent your car in Maine instead of the Boston airport.
The Downeaster trains leave from the Boston North station. All other Amtrak trains leaving or arriving in Boston go to Back Bay and Boston South stations.
My DW and I spent about 16 hours in Maine in late May 2017 when I found a couple of geocaches there.

I've been to Acadia/Bar Harbor more than a dozen times over the years--it's one of my favorite places in the world.

There is nothing wrong with the towns in the lower part of Maine, but if you are looking for outdoorsy stuff like hiking, biking, and kayaking, nothing beats Acadia.

I'm glad Elberko gave Acadia advice. We don't hike and tend to concentrate on finding great lobster shacks so mid-coast Maine is where we head. If you like gardens, Maine Coastal Gardens will give you a good bit of exercise. You might also look into flights to Manchester NH and Portland ME. If you chose MHT, it's a much smaller airport than Boston and an easy drive to the coast. Hopefully cheaper rental cars. If you google a list of Best Maine Lobster rolls and circle the ones you want to try, that would be my choice of route. Make sure they are open weekdays after Labor Day. Most stay open until Columbus Day but sometimes weekends only after Labor Day when the kids go back to school. Instead of whale watching, we prefer a lighthouse cruise. Check to see what might be offered at the Maritime Museum in Bath. We also like the harbor and river cruises out of Portsmouth NH. Instead of hiking, we drive the auto road up Mt. Battie in Camden for the terrific view overlooking the harbor.

We used to own a large inn in the mid-coast area. Southern Maine is okay; they have more beaches but flat terrain and more traffic and suburban sprawl. Just too close to heavy population centers. Midcoast has many beautiful areas (Rockland, Camden); Boothbay, a little tacky, but there are so many wonderful drives and peninsulas in that area. The mountains meet the sea at Camden; that's where the coast takes a decided turn in look and feel. It's another 90 minutes or so to Mt. Desert Island (MDI), Acadia, Bar Harbor. It's a big island (connected by short bridge), with much to see and do. After Labor Day, many of the rich and famous that bring their jets up there have moved on; the kids have gone back to school; almost everything is still open; the busier foliage season hasn't begun; summer-like weather and generally more sun; and you can get some discounts on lodging. We also have lived on MDI, and we think it's one of the most beautiful places anywhere. Highly recommend it!

You could do whale watching from either Boston or Gloucester, MA. Gloucester could be a stop on your way north and there are several ships that go from there, some have free parking which you might not find in Boston.

Acadia is spectacular and you don't need to be a hiker to enjoy it. If you have a National Park pass it will get you in for free.

You can split the stay, maybe 4 nights for Bar Harbor and 3 nights elsewhere. Tourist destinations that are very popular , but not crazy after labor day, include Ogunquit/York/Wells/Kennebunkport...…..or Portland/Cape Elizabeth/Freeport/Sebago Lakes...….or Camden/Rockland/Lincolnville/Mt. Battie.. I would research all of those and decide which appeals to you. There are youtube videos that will give you an idea of what each area is like.

https://www.youtube.com/watch?v=Y847dXBBvcg

We have been going to maine at least once a year for the past 28 years and we prefer Central Maine, or anything between Portland and Wiscasset.
Brunswick, Bath or Freeport make a good base, with Portland a short drive away if occasionally you need something more sophisticated.

There are a lot of easy hikes in the area:

-Popham Beach
-Morse Mountain
-Reed State park
-Wolf Neck Woods
-Dodge Point Nature Preserve
-Pemaquid Watershed area and the lighthouse
All of the above are better at low tide.

Take a drive on Parker Head Road.

A hike up Mount Battie combined with a visit to Camden.

Without a doubt our favourite lobster place is Erica's Seafood in Harpswell.
They don't advertise it but Erica is BYOB place, we usually pick up a chilled alborino at LeRoux in Portland.

In Portland the Shipyard Brewery and tasting room are a lot of fun, so is the Maine Narrow Gauge Railroad.

We have been to Acadia twice, for half a day on both occasion. It is a nice place but I don't know if I would spend most of my time there.

Thank you all for your helpful information.