  By using a Non-linear Electroweak Chiral Lagrangian, including the Higgs,
coupled to heavy quarks, and the Equivalence Theorem, we compute (in the regime
$M_t^2/v^2\ll\sqrt{s}M_t/v^2\ll s/v^2$) the one-loop amplitudes $W^+W^-\to
t\bar t$, $ZZ\to t\bar t$ and $hh\to t\bar t$ (to NLO in the effective theory).
We calculate the scalar partial-wave helicity amplitudes which allow us to
check unitarity at the perturbative level in both $M_t/v$ and $s/v$. As with
growing energy perturbative unitarity deteriorates, we also introduce a new
unitarization method with the right analytical behavior on the complex
$s$-plane and that can support poles on the second Riemann sheet to describe
resonances in terms of the Lagrangian couplings. Thus we have achieved a
consistent phenomenological description of any resonant $t\bar t$ production
that may be enhanced by a possible strongly interacting Electroweak Symmetry
Breaking Sector.
