A can of coke is the same everywhere. Fountain cola varies wildly since restaurants use different levels of carbonation, syrup and freshness. McDonalds fountain coke is the best.
Between countries, a can of Coca Cola varies[1], particularly in the amount of sugar[2], as well as the type (HFCS in the US, cane or beet sugar in most other places).
Well ackshully, It's getting popular in America to get "Mexican Coke" (which is bottled, not canned so your point can still stand) because it can use cane sugar instead of HFCS:
