I want to marry a girl who seems to be good, but have been advised against it by a Sufi Shaykh who claims that my future with this girl will not be good. Please advise.

If the "Sufi Shaykh" cannot give you concrete evidence that your future with the girl is likely not to be good, ignore his prediction which would then fall under fortune telling which is itself shirk, and go ahead and marry the girl after making Salaatul Istikhaarah.