Gotoquiz has a surprisingly accurate quiz about US accents I’ve been clamoring to see for years, after being subjected to quizzes that ask about how I call buckets and pillbugs. Predictably, I got Northeast. I don’t sound like a native speaker of any kind, and I have an online sound sample that proves it, but I don’t have any American vowel merger except this of the British /A/ (“cart,” “father,” “balm,” “calm”) and /Q/ (“cot,” “bother,” “bomb,” “com”) vowels, which to the quiz is what matters.
On the other hand, outside the US the quiz will be completely inaccurate for obvious reasons. Brits will probably get pegged as Northeasterners. Katie, whose accent is 100% Ontario, was pegged in the North Central region, because she has the same vowel mergers and the same Canadian raising as Minnesotans; but her vowel shifts are characteristic of Canada rather than the Old Northwest, so you’ll never confuse her with William H. Macy on Fargo.