  The seesaw extensions of the Standard Models are well motivated in explaining
the tiny neutrino mass. In the process these models predict extra heavy
Majorana neutrino, charged lepton and charged scalars depending on the
scenarios. Distinguishing such scenarios at the colliders would be one of the
first goals if we receive some hint of those. We show how various leptonic
colliders can play a role of complementarity in segregating such scenarios and
the angular distributions can be instrumental, which carry the information of
the matrix element. The $\ell^-\, \ell^-, \ell^+\, \ell^-\, \ell^{\prime\, +}
\ell^-$ colliders are explored in investigating such possibility via a PYTHIA
based simulation. We emphasis on muon collider and comment on the prospect of
$\mu\,e$ collider as well.
