Like what others had mentioned, only EPL3 is a micro 4/3 camera, the others are not.
Of the three... Canon's had the least native lenses available (only 2) with adapter she could fit the EF and EF-S lenses, but up till now, no one know how was the performance if fitted with adapter and using EF and/or EF-S lenses. The focusing speed of Canon's EOS-M is not amazing as was seen from youtube video, but for normal usage it is good enough. I believe that among the three, EPL3 should have the fastest focusing speed.
Of the 3, EPL3 had the smallest sensor (x2 crop factor) and in theory high ISO noise performance is going to be the worst. It also has the least pixel (12MP as compared to Canon EOS-M - 18MP and NEX-3n - 14MP).
Like what Raskhae had mentioned, all three are excellent camera, you would have to go to the shop and have a feel of them (Canon EOS-M is not out yet though), then see which one you like best.