I have seen rattle can that looks ok. But it wont look as good as done with a gun. Take an auto body class at a votech or something.
If do go through with it try and put as little primer as possible and keep ig wet when putting on. If you dont you will have to do more wet sanding and get orange peel.
You need to tac rag after coats to get good results
Do NOT use bondo ever. For a bumper especially. 3m makes good bumper repair products or get a plastic welder. There like 70 bucks