A Facebook group called "100,000 Strong for Bringing Back Mega Man Legends 3" is rallying the troops to let Capcom know that people want this cancelled project back on track. I am a cynical man and I see little that online petitions can achieve, but sod it -- if you give a crap, hit the "Like" button.
Capcom has endured a lot of hatred for the cancellation of Mega Man Legends 3 and it's obvious that many gamers have felt badly stung by it. The group is a little short of its ambition to get 100,000 gamers together -- in fact, it's currently under 5,000 -- but it made most of its gains in a single night, so this is quickly gathering steam.
Whether Capcom will listen or not is another story, but it has gone on record as saying that audience interest was a deciding factor, so this is a chance for the audience to make itself heard. Go prove you give a damn, if you do.