To which I say: Bunk.
Their source is a British site called Coventry Telegraph which has gone out and found a bunch of online polls and such where fans are overwhelmingly picking Smallville star Welling as their choice for the man to play Superman in the next movie. One poll has actually gathered 1,482 names voting for Tom Welling as their man to don the blue tights and red cape.
Well, damn, in that case I'd say it's a lock.
Anyone who knows anything about the way studios really work will tell you that fan preferences have pretty much nothing to do with movie casting decisions. Sometimes they make a good call (Michael Keaton as Batman, Robert Downey Jr. as Iron Man) and sometimes they don't (Ben Affleck as Daredevil, George Clooney as Batman).
In each case fan desires had nothing to do with the choice.
These sort of polls really do nothing more than make the people adding their names to them feel like they've "done something." How many polls and campaigns have we seen trying to influence Hollywood that actually succeeded? Besides the classic example of the original Star Trek back in the late 1960's (which was cancelled after the second season but was brought back for a third after an avalanche of fan mail), and the recent (and short-lived) reprieve for CBS' Jericho, nothing else comes to mind.
At this point there is no script (despite the noises Mark Millar is out there making), no director and Tom Welling is NOT being considered to play Superman in the followup to Superman Returns.