Unlike the Spark and Sonic which have a somewhat more minivan-like shape, the Onix has more conventional proportions.
It's only fitted with 3-cylinder engines between 1.0L and 1.2L according to each of the markets where it's already available, including turbocharged versions. Brazil only gets the 1.0L ones, while a naturally-aspirated 1.2L is bound to export for Argentina only with a manual transmission while the turbocharged 1.0L is also available with automatic transmission. AFAIK the turbocharged 1.2L is only available with the automatic.
It was initially released in China as a sedan, which is the only bodystyle available there and in Mexico.