Starting with "A":
* Argentina
* Australia
Starting with "B":
* Bulgaria
Starting with "C":
* Canada
* Columbia (South America)
* Croatia
Starting with "E":
* Ecuador
Starting with "G":
* Guatemala
* Guyana
Starting with "I":
* India
* Ireland
Starting with "M":
* Malaysia
Starting with "N":
* Nigeria
Starting with "P":
* Panama
* Portugal
Starting with "S":
* Slovakia
* Slovenia
Starting with "U":
* Uruguay
Starting with "V":
* Venezuela
This is not an exhaustive list, and there are many other countries with three syllables, depending on pronunciation variations.