You could use \tikzmark.
I think there's a way to calculate the exact positioning automatically, but it's above my level of knowledge.
If you have few cells to cross out, you could calculate it manually with trial and error (like I did) without big problems.
\documentclass{book}
\usepackage{tikz}
\usetikzlibrary{tikzmark, calc}
\usepackage{array}
\usepackage{multirow}
\setlength{\extrarowheight}{2pt}
\begin{document}
\begin{tabular}{|c|c|c|}
\hline
foo & bar & baz \\
\hline
\multicolumn{2}{|c|}{\tikzmark{smc}\hfill double\hfill\tikzmark{emc}} & B \\
\hline
C & D & \tikzmark{smr}\multirow{2}{*}{$\delta$}\tikzmark{smr} \\
E & F & \\
\hline
\end{tabular}
\begin{tikzpicture}[overlay,remember picture]
\draw ($(pic cs:smc)-(\tabcolsep,3.6pt)$) -- ($(pic cs:emc)+(\tabcolsep,10.4pt)$);
\draw ($(pic cs:smr)-(16pt,17.6pt)$) -- ($(pic cs:emr)+(-3.7pt,2.2pt)$);
\end{tikzpicture}
\end{document}

Note that the \tikzmark must be put inside the \multicolumn, see here.