It really doesn't matter that it's a pusher or not for electric power. You just use a regular prop mounted backwards on the motor and it is now a pusher prop.

We'd need more specs on what motor it is. And even then typically there's a little testing needed to sneak up on the power level you want without burning out the motor. So don't expect a solid answer.

The other thing I see is that you are running a 920Kv motor from a 3S pack. At that Kv and voltage the motors are usually rated more for larger and slower turning props. Like 9 to 11 inch diameters. Such motors are more useful on powered gliders or 3D flat foamie models that want big fine pitch props for flying and don't want the prop size to make the motor burn out. But for something like the Astro Blaster I'd imagine you would want more speed. For that you want a motor with a Kv value up more around the 1800 to 2000 range so it can run a smaller prop at higher RPM and really make the AB zip.

So you might have the wrong sort of motor for what you are doing.

Finally this is more about picking the prop size than about canard designs. Don't be afraid to start a new thread instead of pulling up an old one. In this case it would have made more sense.