Listen to Ewan in the scene where he talks to Boss Nass and it’s pretty clear he’s taking more than a page from Guiness’ mannerisms and speech patterns. He even requested Lucas compile every scene of Obi Wan on a tape that he watched almost every day before shooting.
If you’re trying to cast a character played by a single actor, the biggest reference you should be going by is how that actor looked and preformed. Otherwise it obscures and lessens the importance of that original performance and the character becomes less defined for the worse.
But in any case it’s better to just wait and see how things turn out when the movie actually goes into production.
Jedit: Also I guess you haven’t watched the bonus feature where they literally boast about how cool it is that Ewan is so much like Alec in appearance and presence.