from NZ's perspective, I think most will be able to sense variation between New York and Midwest.
Most Americans would also, if given a few moments of reflection (a lot of people never think about it). I make a habit of listening for dialects in conversation among Americans as well as Brits (the only other English speakers I hear a lot of on TV -- I'm addicted to British productions of classic literature). My Dutch friend of one day, in Eastern Canada at some sort of post-graduate consortium, had traversed Canada east to west. He had traveled a great distance in the US before arriving at his amazed conclusions about our citizenry being able to go a thousand miles (and more) without encountering language barriers. He hadn't been to the South, or the NE, yet, as I recall, where he would have found some dialects that are not as fluidly understood.
I have a relative who married a man from New Jersey and I never could understand more than one of four of his words. I got very tired of asking him to repeat almost every sentence and he never would try to enunciate so I spent a lot of time nodding and smiling while he talked. I asked him what we sounded like to him. He said, "You pronounce every syllable very clearly." YES! And why should that not become a habit? ???
I personally found it hard to distinguish the accents of people in urban Ontario and General American, although if you put a Canadian next to an American, it will be obvious to a NZ ear which one is Canadian. Interestingly I watched some archives of CBC news from 25 years ago and as recently as the early 1980s it was still possible to detect the quasi-RP accent of CBC newscasters.
Newfoundland or Atlantic Canadian accent is another matter. There is no question to confuse a Newfie with an American. I heard some of them talking and I thought they are from Cornwall or Ireland rather than North America.