Please explain the mechanism of Cannizzaro's reaction

I did not completely understand the mechanism of Cannizzaro's reaction, especially the rate determining step i.e. the hydride transfer step, and the effect of electron withdrawing substituents on this step.
Like, I was taught that the intermediate which donates hydride, would donate hydride more readily when electron donating substituents were attached to carbon atom with the outgoing hydrogen atom, as they would increase electron density on that carbon, and therefore create a "pushing" effect on the outgoing hydride. But in all the questions I have attempted, the answer says that electron WITHDRAWING substituents facilitate hydride transfer.
Please tell how the electron withdrawing substituents affect the hydride transfer, and why. Also, please explain how to determine the products of a crossed Cannizzaro's reaction. Do we determine them using the concepts of the RDS,or otherwise? 


