Why humans? People are concerned about the survivability of human species, and it's certainly a noble goal, but at this point it's outside or technological reach. Preserving life, in the other hand, could be doable. We «just» need to take some prokaryotic cells to one of those planets, assuming they have the right environment, and in some million years you have a complete ecosystem...

Assuming also, of course, that there is not life there already.