Merida is a proper noun that can refer to a city in Spain or a city in Mexico, or a fictional/brand name. It is pronounced with two syllables in common English usage, typically with initial light schwa or short i, then a stressed second syllable, and a final schwa. In Spanish usage, it is closer to meh-REE-dah, with an emphasis on the second syllable and a clear trailing 'a'.
Full pronunciation guide