I feel that the Maritimes are somewhat simplified here, especially Newfoundland and Labrador which has some of the most distinctive accents on the continent, at least among older people.
It's absolutely oversimplified, someone from a small coastal town in Newfoundland does not sound at all like a person from much of the same area labeled "atlantic canadian" in Nova Scotia, or in larger cities like Fredericton or Moncton in NB. Putting basically all of NB, NS and NF as one large pink blob on the map is a drastic oversimplifiaction.
It also seems that whoever created this kind of gave up when figuring out Canadian speech patterns spanning longitude from east to west. Somebody from Kenora or Dryden or Timmins Ontario does not speak like a person from North Vancouver, BC. Vancouver region English is much closer to general west coast as it's spoken in a big city in WA, OR or California.
I'm from Ontario and its very simplified in my experience as well. Maybe the problem is the sample audio clips they have are all 'posh', its not how most people speak. Two large examples I can think of that even have their own wikipedia pages are the Ottawa Valley Twang (https://en.wikipedia.org/wiki/Ottawa_Valley_English) and the 'Torontomans' (https://en.wikipedia.org/wiki/Toronto_slang). I grew up in Toronto, and the latter isn't just something funny you see on tiktok, people actually talk that way.
It's oversimplified for any region whatsoever. You're citing right here what people speak like in big west coast cities but I grew up in California and would have been able to tell apart people who grew up in Anaheim versus San Gabriel Valley versus San Fernando Valley versus West LA, let alone LA versus San Francisco. I couldn't have explained what the difference is but I could have heard it. Everybody will be more attuned to the tiny regional differences of the place they actually come from, but a map like this would be impossible to make if you tried to draw out the boundaries and explanations for 400 million separate regional dialects.
I'd agree completely but this could just be due to logistical constraints of the ANAE, I took a course with Charles Boberg (one of the authors of the ANAE) and he was definitely aware of that, I vaguely recall learning from him that the Newfoundlander accent traditionally doesn't have t/d flapping which is totally unique in North America. Great class, he definitely has an incredible knack for precisely imitating accents.
And right next door, the Maine accent is lumped in with Boston. The differences aren't worth correcting anybody unless you're talking about a project like this.
I'm not an expert on accents or anything but I think you can hear it in "dinner". Boston is the typical "R's don't exist" thing. Maine is more like "dinnyah" - your jaw kicks back a bit.
I am not American but can hear slight differences between Maine and Boston. Urban accents are often different to their hinterland, let alone those with different formative influences.
Maine has multiple distinct accents, though like the parent said, it's not worth making the distinction unless it's for a project like this.
In southern Maine, the accent is moderate and is more of a general northern New England accent. Yahd = yard, that kind of thing.
The iconic Maine accent is the Downeast accent and is still kicking up/down there. It's kind of nasally and has a lilt to it. You have to dig through a morass of influencer content on youtube to find an authentic example of it, but this is a good one: https://www.youtube.com/watch?v=FZDpx1aLovc
But there are a number of different accents throughout Maine. My favorite without a doubt is the accent in way northern Maine, from the Allagash Valley. It's just a pleasant accent. This is a good example: https://soundcloud.com/mpbn/troy-jackson-allagash-logging
Just an update to this. I realize I misspoke and misnamed where that last accent comes from. It's too late for me to edit the original comment, so I'm just going to drop it in here. There's no such thing as the Allagash Valley, only the St. John Valley.
It also seems that whoever created this kind of gave up when figuring out Canadian speech patterns spanning longitude from east to west. Somebody from Kenora or Dryden or Timmins Ontario does not speak like a person from North Vancouver, BC. Vancouver region English is much closer to general west coast as it's spoken in a big city in WA, OR or California.