Resonant tunneling is known to emerge in ballistic electron transport in a quantum waveguide with two narrows (constrictions). Here we present results of numerical simulations of electron transport in a system consisting of two identical resonators produced by three narrows in a quantum waveguide. It is shown that, at small electron energies, the resonance peaks of one-resonator system split and the peaks width and their separation depend on the diameter (width) of the narrows. The processes of high energy electron transport, where the role of multichannel scattering with changes of transverse channels (quantum states) becomes substantial, have been investigated. In addition, resonant tunneling in a quantum waveguide with N + 1 delta potential barriers which produce N resonators has been considered. Numerical simulations show formation of band structure and the bands parameters-dependence on the potential barriers, which confirm the possibility of making quasi-one-dimensional crystal in a quantum waveguide with a number of narrows. The results of the study may find potential applications in designing various resonance devices based on quantum waveguides.