I think it can be a good exercise to at least start thinking about it as this stage. That way you can spend time reading up on possible projects, and investigating different sub-fields. But the reason most students don't take this on until their final year is because they're still developing the tools they need.
Some things you might want to try are talking to professors, graduate students, TAs, and current senior students about what projects they have seen in the past or are currently working on. You can also start reading journals such as Physics Today to get a feeling about some of the more interesting research currently under way in the world.
Other things to keep in mind might be to look for a project that is going to give you a marketable skill (programming, experience with electronics, etc.) for when you graduate and perhaps an opportunity that could extend into graduate work.