Trouvé [sur Stackexchange](https://tex.stackexchange.com/questions/173463/use-textsc-for-name-and-section-in-moderncv) ! !
« There are only a few sans serif typeface families with a small caps font. Latin Modern Sans, that's used by default with moderncv, definitely hasn't it.
So, either you change the setup so that the CV is typeset with a serif font (which isn't a bad idea, in my opinion), you have to choose a font family having the required shape. For instance,
`\usepackage[scale]{tgheros}`
will do, but it will typeset your CV in (a clone of) Helvetica ».