Can i use two AC sources to power one load?
Yes, but it depends on your inverter. Many of the high quality inverters that have an AC input have a mode just for that. When the generator is running, they will meter how much power is being used and if it exceeds the internal (adjustable) set point power level of the generator, it will "support" the generator. i.e. it will produce just enough power to keep the generator loaded to the set point that you program. When large loads need to be run, the inverter augments (supports) the AC source, adding inverter and battery power to ensure that the loads receive the power they demand.

Outback power calls this mode "support mode," Schneider (previously known as Trace, or Xantrex) calls this mode "Generator Support," Magnum Energy calls it "Load Support."

Note from Outback power support- 


  IMPORTANT: 
  If the AC loads exceed the amperage limit setting, the inverter will draw energy from the 
  batteries. If the loads are sustained, the batteries may discharge to the point of Low 
  Battery Cut-Out and the inverter may shut down with a Low Battery error.  To prevent the loss of backup power, load use should be planned accordingly.


The only thing that I see that could be a problem is that you specified that (if I understand you correctly) you wanted it to primarily draw off of the solar, and supplement with the generator. The inverters however are designed to primarily pull off the generator and supplement with the solar/battery power. This is so that you don't drain your batteries too much. Generators are actually much more energy efficient (more power per fuel consumption) when they are loaded down (as opposed to running near idle) so most people will advise to primarily use the generator power while it is running so that your batteries will be closer to full when you turn the generator off. But I guess if you wanted to use more of your battery, you could set the "max generator power" lower so that the inverter offsets more of the power.

Edit based on comments below: Here is a brief illustration to show a way you can do this. 
MAKE SURE to have a large enough load. 3kW should be enough but too much is better than too little. Program the inverter into grid interactive mode (I'm not sure what that's called for schneider). Just program it the way the manual says to in order to sell power back into the grid. It won't successfully push any power back into the grid (or generator) because your resistive load will fully consume it. The only hurdle that might arise is finding a high amperage 220 outlet to plug it into for your demonstration. I don't think this method would work with a 1kW generator... just too small to support the load.

P.s. This sounds like a pretty expensive school project but it should work and when you are finished with it you can use all the parts for something useful (except maybe the resistive load).