Constrained Hamiltonian systems are investigated by using Gu¨ler’s method. Integration of a set of equations of motion and the action function is discussed. It is shown that the canonical path integral quantization is obtained directly as an integration over the canonical phase‐space coordinates without any need to enlarge the initial phase‐space by introducing extra‐ unphysical variables as in the Batalin‐Fradkin‐Tyutin (BFT) method. The abelian Proca model is analyzed by the two methods. © 2004 American Institute of Physics