3 inch props actually makes it easy. You'll be able to use brushless inrunner motors without gear boxes, but you'll need pretty beefy ESCs.

I'd recommend checking out the parts available at Hobby City and staying with a smaller 20mm or 24mm inrunner. The Hextronic (HXT) and KD brands look like good values. Just remember that higher KV motors turn faster while lower KV motors turn larger props. I'd start with a medium KV rated inrunner like the Hextronic 2040 2900KV motor.

You'll want to mate them with 30 or 40 amp brushless speed controllers. Those 3 inch props on direct drive from an inrunner will pull a lot of current. Again, Hobby City offers some very good speed controllers at very fair prices.

I'd try running each setup from seperate 2S LiPos and then experimenting with 3S or 4S batteries if your testing indicates you need more power.

Hopefully the size and weight of these components will fit your design parameters. For turning a pair of three inch props, however, I'm confident that these are good general recommendations.

Good luck and good shopping!