Your application can pass ATSUI features and variations to MLTE functions and have them applied to a selection. This, like building the Font menu, requires your application to be aware that it is running on a system that has ATSUI, and further requires you to use some of the moderately complicated ATSUI functions.
MLTE does not provide a human interface that allows a user to view and select font variations and features on a per font basis. However, your application can create a user interface that displays font variation and font features. Then you can use MLTE functions to get and set font features and font variations in response to items your user changes in the interface your application creates.