[mapt]

They are the same phoneme for me in US Eastern suburbia, the only difference is in a subtle shift in the length that you drag it out. "merry" is faster than "marry" which is sometimes but not always faster than "Mary". Most UK accents seems to drag the proper name out an additional beat, and for some of them there's a slight pitch shift that sounds like "ma-ery", at its most extreme in Ireland (this is one early shibboleth by which I recognized Irish people before I really picked up on the other parts of the accent).