In the second work of this series, we analyse the connection between the availability of gas and the position of a region with respect to the spatially resolved main sequence (MS) relation. Following the procedure presented in Paper I we obtain 500pc scales estimates of stellar mass and star formation rate surface densities ($Sigma_{star}$ and $Sigma_{rm{SFR}}$). Our sample consists of five face-on, grand design spiral galaxies located on the MS. Thanks to HI 21cm and $^{12}$CO(2-1) maps, we connect the gas surface densities and gas fractions to the observed star formation properties of each region. We find that the spatially resolved MS ($sigma=0.23$ dex) is the combination of two relations: the Kennicutt-Schmidt law ($sigma=0.19$ dex) and the molecular gas MS (MGMS, $sigma=0.22$ dex); $Sigma_{star}$, $Sigma_{rm{SFR}}$ and the surface density of the molecular gas, $Sigma_{rm{H_2}}$, define a 3D relation as proposed by citet{2019ApJ...884L..33L}. We find that $Sigma_{rm{H_2}}$ steadily increases along the MS relation, varies little towards higher $Sigma_{rm{SFR}}$ at fixed stellar surface densities (not enough to sustain the change in SFR), and it is almost constant perpendicular to the relation. The surface density of neutral gas ($Sigma_{rm{HI}}$) is constant along the MS, and increases in its upper envelop. $Sigma_{rm{SFR}}$ can be expressed as a function of $Sigma_{star}$ and $Sigma_{rm{HI}}$, following the Equation: $logSigma_{rm{SFR}}$ = 0.97$logSigma_{star}$ + 1.99$logSigma_{rm{HI}}$ - 11.11. Finally, we show that f$_{rm{gas}}$ increases significantly towards the starburst region in the $logSigma_{star}$ - $logSigma_{rm{SFR}}$ plane, accompanied by a slight increase in SFE.
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