I use font now which will not work if I do not use `unicode-math`. Which means if I want to be breqn, I have to change my font. But I like the font I am using now. Here is an example
\documentclass[12pt]{book}
\usepackage[mathit=sym,bold-style=ISO]{unicode-math}
\setmainfont[Ligatures={Common,Rare,TeX}]{TeX Gyre Pagella}
\setmathfont[Scale=MatchUppercase]{Asana Math}
\usepackage{amsmath}
\usepackage{breqn}
\begin{document}
\begin{dmath}
2 x^{2} = 0
\end{dmath}
\end{document}