  Classical Cepheids are essential objects in the study of stellar evolution
and cosmology; however, we know little about their magnetic properties. We
report the detection of Stokes $V$ features interpreted as Zeeman signatures in
four classical Cepheids using high-resolution spectropolarimetric observations
obtained with ESPaDOnS at CFHT. Eight observations of $\eta$ Aql were acquired
in 2017 covering its 7.2 d pulsation period, and single observations of
Polaris, $\zeta$ Gem, $\delta$ Cep and RT Aur were obtained in 2020 as part of
our ongoing systematic survey. We use mean circular polarization Stokes $V$
profiles generated using the Least-Squares Deconvolution procedure to diagnose
Zeeman signatures and measure mean longitudinal field strengths $\langle
B_{z}\rangle$. We detect magnetic signatures across all pulsation phases of
$\eta$ Aql ($-0.89\pm0.47$ G$\,<\langle B_{z}\rangle<1.27\pm 0.40$ G), as well
as in the single observations of Polaris ($0.59\pm0.16$ G), $\zeta$ Gem
($0.41\pm0.16$ G) and $\delta$ Cep ($0.43\pm0.19$ G). The Stokes $V$ profile of
Polaris is detected at extremely high S/N and implies a complex magnetic field
topology. It stands in stark contrast to all other detected Stokes $V$
profiles, which show unusual approximately unipolar positive circular
polarization lobes analogous to those observed in some Am stars.
