  We explore the possibility of using the B-type polarization of the CMB to map
the large-scale structures of the Universe taking advantage of the lens effects
on the CMB polarization. The functional relation between the B component with
the primordial CMB polarization and the line-of-sight mass distribution is
explicited. Noting that a sizeable fraction (at least 40%) of the dark halo
population which is responsible of this effect can also be detected in galaxy
weak lensing survey, we present statistical quantities that should exhibit a
strong sensitivity to this overlapping. We stress that it would be a sound test
of the gravitational instability picture, independent on many systematic
effects that may hamper lensing detection in CMB or galaxy survey alone.
Moreover we estimate the intrinsic cosmic variance of the amplitude of this
effect to be less than 8% for a 100, deg^2 survey with a 10' CMB beam. Its
measurement would then provide us with an original mean for constraining the
cosmological parameters, more particularly, as it turns out, the cosmological
constant Lambda.
