  We propose a simple and model-independent procedure to account for the impact
of the nuclear modification of the gluon density as encoded in nuclear
collinear PDF sets on two-to-two partonic hard processes in proton-nucleus
collisions. This applies to a good approximation to quarkonium, D and B meson
production, generically referred to H. Our procedure consists in parametrising
the square of the parton scattering amplitude, A_{gg -> H X} and constraining
it from the proton-proton data. Doing so, we have been able to compute the
corresponding nuclear modification factors for J/psi, Upsilon and D^0 as a
function of y and P_T at sqrt(s_NN)=5 and 8 TeV in the kinematics of the
various LHC experiments in a model independent way. It is of course justified
since the most important ingredient in such evaluations is the probability of
each kinematical configuration. Our computations for D mesons can also be
extended to B meson production. To further illustrate the potentiality of the
tool, we provide --for the first time-- predictions for the nuclear
modification factor for eta_c production in pPb collisions at the LHC.
