Answer
The proton will also pass through with no deflection.
Work Step by Step
Let $B$ be the magnitude of the magnetic field. We can write an expression for the force on the electron due to the magnetic field:
$F_B = q~v_0~B$
By the right hand rule, this force is directed upward.
Let $E$ be the magnitude of the electric field. We can write an expression for the force on the electron due to the electric field:
$F_E = E~q$
This force is directed downward.
Since the electron experiences no deflection, the magnitude of the two forces must be equal.
Note that the magnitude of the two forces on the proton will also be $F_B$ and $F_E$. By the right hand rule, $F_B$ is directed downward while $F_E$ is directed upward. Since the magnitudes of these two forces are equal, the proton will also pass through with no deflection.
