$\underset{\text{trimethyl acetaldehyde}}{CH_{3} -\underset{\overset{|}{CH_{3}}}{\overset{\underset{|}{CH_{3}}}{C}}- \overset{\underset{|}{H}}{C}=O} $
$\underset{\text{ acetaldehyde}}{H_{\alpha} -\underset{\overset{|}{H_{\alpha}}}{\overset{\underset{|}{H_{\alpha}}}{O}} -\overset{\underset{|}{H}}{C} =O}$
$\underset{\text{formaldehyde}}{H -\overset{\underset{|}{H}}{C}=O}$
Cannizzaro reaction is given by only those aldehydes which do not have $\alpha$-hydrogen atom. As such acetaldehyde will not give Cannizzaro reaction.
