\usepackage{mathspec}
\setmainfont{Inria Sans}[Scale=MatchLowercase]
\setsansfont{Inria Sans}[Scale=MatchLowercase]
\setmathfont(Digits,Latin,Greek,Symbols)[Scale=MatchLowercase]{Inria Serif}
\setmathrm[Scale=MatchLowercase]{Inria Sans}
\usepackage{mathastext}