The Calgary Herald's a good source (that's where the blog got its info from) and there have been similar reports. It makes sense since the first Superman and Superman III also were shot in part out there.
The sad part about the casting announcement is the maniacs have already come out of the woodwork. Some guy posted a comment on a Zap2It blog report about the casting calling Cavill a terrorist and making a death threat, apparently because he was mad that an American wasn't cast. I reported the post to the authorities, but it's a shame that casting a frelling movie is making some people think of violence. God help us when the time comes to recast Batman again.