I doubt that will ever happen - for a couple of reasons.
1) The distance to even the nearest extra-solar planets is so immense that, with our present technology, it would take hundreds of thousands of years just to reach the nearest planets. Of course, there are likely many thousands of Earth-like planets in our galaxy alone, but most, if not all, are likely to be forever beyond our physical reach.
2) If, by some cosmic good fortune, a planet capable of sustaining human life was found within our 'range' i.e. if we develop spacecraft capable of 1/2 light speed, and the planet was within say 50 light years distance (note that our galaxy is some 100,000 light years across), then we'd have an extra problem to think about - if another planet is capable of sustaining life such as that found on Earth, the chances are that it will already be inhabited as abundantly and with the sort of diversity as here on Earth - the small, privileged elite who were able to pay for a berth on the interstellar escape ship (probably only the super-rich, the super-powerful, and the most recent winner of Big Brother) would find themselves as an alien force, presumably unannounced, and almost certainly unwelcome. If they landed on an Earth-like world before the dawn of intelligent civilisation, they might have to contend with a Jurassic Park-style nightmare scenario of terrible, vicious carnivorous lizards who hunt in packs and would have human beings for breakfast without even batting an eye-lid... if we showed up to find a highly advanced civilisation already present, we could forget about taking over the planet and saving the human race... either way, it would be extremely difficult for humankind to get the necessary foothold unless we sent vast numbers of people - unfortunately, that would require a level of international cooperation and understanding that the human race is barely capable of now, let alone in 200 years time when wars will rage on this planet over increasingly rare natural resources....
