  Generalized parton distributions (GPDs) encoding multidimensional information
of hadron partonic structure appear as the building blocks in a factorized
description of hard exclusive reactions. The nucleon GPDs have been accessed by
deeply virtual Compton scattering and deeply virtual meson production with
lepton beam. A complementary probe with hadron beam is shown to be the
exclusive pion-induced Drell-Yan process, $\pi^- p \to \mu^+ \mu^- n$, as
demonstrated by recent theoretical advances on describing this process in terms
of QCD factorization as the partonic subprocess convoluted with the nucleon
GPDs and the pion distribution amplitudes, and by the feasibility study for its
measurement via a spectrometer at the High Momentum Beamline being constructed
at J-PARC in Japan. We also discuss the possible soft partonic mechanisms
beyond the QCD factorization framework, and present an estimate of the soft
mechanisms at J-PARC kinematics, making use of dispersion relations and
quark-hadron duality. Realization of the measurement of the exclusive
pion-induced Drell-Yan process at J-PARC will provide a new test of QCD
descriptions of a novel class of hard exclusive reactions, and also offer the
possibility of experimentally accessing nucleon GPDs at large timelike
virtuality.
