  Young & massive stellar clusters (SCs) are a potential source of galactic
cosmic rays up to very high energies as a result of two possible acceleration
scenarios. Collective stellar winds from massive member stars form a wind-blown
bubble with a termination shock (TS) at which particle acceleration to PeV
energies may occur. Furthermore, shock acceleration may occur at SNRs expanding
inside the bubble. By applying a model of CR acceleration at both the wind TS
and SNR shocks to catalogues of known SCs derived from Gaia DR2, we identify
the most promising targets to search for evidence of PeVatron activity.
Predictions for the secondary fluxes of gamma-ray and neutrino emission are
derived based on particle acceleration at the collective wind TS and the
subsequent hadronic interactions with the surrounding medium. Predictions from
our modelling under baseline and optimistic scenarios are compared to data,
finding consistent results. We estimate the detection prospects for future
gamma-ray and neutrino experiments. We find that degree-scale angular sizes of
the wind-blown bubbles are typical, that may pose a challenge for experimental
detection. A shortlist of the most promising candidates is provided, with an
anticipated flux range. Of order 10 SCs may be detectable with future
facilities, and 1-5 could be currently operating as PeVatrons. Of these, three
gamma-ray detected SCs have data within our predicted range. Our model can
consistently describe gamma-ray measurements of SC emission. Several further
as-yet-undetected SCs offer promising targets for future observations, although
the flux range allowed by our model can be large (> factor 10). The large
angular size of the wind-blown bubble may lead to low surface brightness
emission, worsening the problem of source confusion. Nevertheless, we discuss
how further work will help to constrain SCs as PeVatron candidates. (abridged)
