  We consider a non-supersymmetric USp Yang-Mills Chern-Simons gauge theory
coupled to fundamental flavours. The theory is realised in type IIB string
theory via an embedding in a Hanany-Witten brane configuration which includes
an orientifold and anti-branes. We argue that the theory admits a magnetic
Seiberg dual. Using the magnetic dual we identify dynamics in field theory and
brane physics that correspond to various phases, obtaining a better
understanding of 3d bosonization and dynamical breaking of flavour symmetry in
USp QCD$_3$ theory. In field theory both phases correspond to magnetic 'squark'
condensation. In string theory they correspond to open string tachyon
condensation and brane reconnection. We also discuss other phases where the
magnetic 'squark' is massive. Finally, we briefly comment on the case of
unitary gauge groups.
