Virtually any aircraft can fly from one spot on the globe to another. Your question must be qualified with respect to ETOPS, non-stop service, passenger service, or some other qualification of the Federal Aviation Regulations.
E.g. a 727 is smaller than a 757, but 727s have operated Part 135 (commercial passenger)operations across the Atlantic. But they have three engines. And it was not non-stop. A320s can cross the Atlantic too but usually only as a non-passenger ferry flight. A little Cessna can also go across the Atlantic but not as a passenger flight nor obviously non-stop.
P.S. ER does not mean that a plane is certified for ETOPS across the Atlantic. It merely means that it is a longer-range version of a previous model.
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