To accuratly judge what size of pump you will need u need to get a rough estimate on what your head height will be. You start measuring your head hieght at water level from the pond surface that the pump is in. Head height does not just mean how far the pump has to pump verticly. For instance every 10ft of horizontal piping you have, that counts as 1ft of verticle head. Also fittings such as T's, 45 and 90 degree elbows also add to the head height.
To avoid pressure losses though fittings i would use flexible
PVC, and with the waterfall you are planning i would use at least 2". Using 2"
PVC will allow your pump to work easily because it doesnt have to pump the water through very fast. It is the same effect as trying to drink something through a stir straw.....it doesnt really work.
Another advantage of using the 2"
PVC is that you can take advantage of a lower pressure more energy efficent pumps such as Pondmaster(magdrive), Oase, etc. For instance Oase makes a pump that flows 2100gph and only uses 100watts of power....thats like a light bulb. So to answer your question yes you can use a regular pump, your dont need a waterfall pump for a waterfall. If you plan on having an actuall 3ft wide path that the water will be flowing over you will need a pretty good sized pump. When it comes to choosing a pump size, I would look at around the 3000-3600gph range for a waterfall that wide, and that would be 3000-3600gph at your head height. A good estimate is to get about 1000-1200gph for every 1ft of waterfall width.