There has not been a Bessa R3 rangefinder, just the R3A. Leica made an R3 SLR back in the 70's.
Current Bessa rangefinders are the R2A and R3A as per the thread Grant mentions. They replace the R2, and have aperture priority automatic exposure. The difference between the R2A and R3A is the viewfinder magnification and widest built-in viewfinder frames, 35mm for the R2A and 40mm for the R3A.
Cosina has also recently made the Voigtlander Bessa R2, R, T, and L model rangefinders (although the L is not a true rangefinder, uses estimation focusing and auxiliary viewfinders).
See cameraquest.com for full information. Some of the pages are a little dated, and so some older comparisons/claims are no longer strictly true, but if you look through the site, you get a good idea of the model features and time sequence.