  This note presents the prospects of searches for new heavy resonances
decaying to diboson (WW) and measurements of electroweak WW/WZ production via
vector boson scattering (VBS) in association with a high-mass dijet system in
the $\ell\nu qq$ final states ($W\to\ell\nu$, $W/Z\to qq$). The prospects are
presented for an integrated luminosity of 15 ab$^{-1}$ of proton-proton ($pp$)
collisions at $\sqrt{s}=27$ TeV with an ATLAS-like detector simulated in the
Delphes framework. The cross-section measurement of the electroweak $WW/WZ$
production in VBS processes is expected to reach the precision of $\sim$2-3\%,
improving the expected accuracy at the HL-LHC by a factor of 2. Prospects are
presented also for the separation of the longitudinal component of the
electroweak $WW/WZ$ production, showing the expected significance of
$\sim3\sigma$ is reached with 3 ab$^{-1}$ for the single $\ell \nu qq$ channel
and $\sim5\sigma$ for all the semi-leptonic channels combined. The diboson
resonance searches are interpreted for sensitivity to a simplified
phenomenological model with a heavy gauge boson. With 15 ab$^{-1}$ of $pp$
data, the discovery reach for the new resonance is extended to 8 TeV.
