There are various ways you can repair the bumper. But depending on the extent of the damage it is probably going to be ABS Plastic Welded or spliced with either a plate or fibreglass. Bondo/Filler alone will not suffice, filler is basically a hard, brittle but non-flexible plastic. For this reason its not suitable as a structural material, as any movement in the filler will crack the paint on top of it.
Plastic welding takes some time to master, whereas fibreglass is a lot more forgiving. If you're confident with this sort of work, I would personally try and repair it using fibreglass. This will reinforce the bumper from behind which you can then bondo on top before painting.
Good luck mate