To find out and enthalpy of a reaction using bond energy we use the formula
$$\Delta H = \sum\Delta_\mathrm{bond}H_\mathrm{reactants} - \sum\Delta_\mathrm{bond}H_\mathrm{products}$$
since we use all the individual $\Delta H$ of the bonds to calculate the enthalpy, e.g.
$$\Delta H_\ce{C2H6} = 2\Delta_\mathrm{bond}H_\ce{C-C} + 6\Delta_\mathrm{bond}H_\ce{C-H}$$
But if a molecule is in resonance, how is the bond enthalpy taken? For example,
Is bond enthalpy the sum of the bond energies of that canonical structure which is the most stable or the average of all canonical structures or something else?