How to determine stresses induced to a single stage pump shaft

I would like to identify and determine the stresses induced to a single stage pump shaft so as to determine if the current used shaft is suitable for the application.
Can I use the hydraulic power (P=rho*g*H*Q) and convert it to radial as well as the component axial force exerted to the impeller in order to determine the bearing required for the application
can I use the same fluid power to determine the stresses induced to the shaft

just to give a broad backround we are currently encountering frequent shaft shearing/breakages just behind the pump impeller, the suspicion is that the cause is pump cavitation, however, it is also good to determine whether the selected shaft is suitable for the application.

your urgent comments and advice will be highly appreciated.