i agree with John, unless there are other factors, as there often are. Such as if he has different employees in the different businesses, for just one example, and he wants to take one into the ownership of one of the businesses. I know you can all think of a dozen other reasons why he might want to keep the two businesses separate. I'd just suggest starting by talking to the client about what his long range plans are, and why he's thinking of multiple corps. Let him do most of the talking until you get a feel for what is worrying him, what he's got in the back of his mind. Then you can advise him how best to get to where he wants to be.
I think we sometimes push clients into the setup that WE think is best for them, before we find out enough about what their real goals are. I know I did a few times.