That's an interesting thought that I hadn't considered. Clearly, there was enough clout to bring over, at least, one of the original leads, since that's what happened, but I wonder if the producers had had to choose between bringing Jackman or Gabrielle over, what they would have done. Jackman seemed to have gotten the lion's share of the reviews (or that could just be my memory being faulty) and Gabrielle didn't get strong reviews in New York, so I'm guessing that, had he been available and willing to do it, they'd have brought Jackman to New York and cast an American actress as Laurey.
I remember almost nothing about Gabrielle's performance in New York, except that she got a lot of publicity out of also dancing the ballet. She was widely publicized as being the first actress to do so, but, of course, we all know now, and probably knew then, that that was not true.