Wrong, wrong and some more wrong is all one can say for this piece which has not just ended up mixing a couple of stories together but also suffers big time due to someone's figment of imagination, going an extra mile that has only ended up making it all a 'bhel-puri' of sorts.
So let's start taking back this statement and state some facts:
# Is there a film called Tanu Weds Manu? Answer -
# Is Maddy acting in it? Answer - Yes
# Is Shahana part of the film? Answer - NO
# So who plays Tanu? Answer - Well, that's yet to be decided!
# Is Nikhil Advani directing Maddy in this film? Answer - No
# So who is the director of the film? Answer - Aanand Rai of Strangers (Jimmy Sheirgill, Kay Kay Menon) fame
# So is there a way where Nikhil Advani and Mukesh Talreja are related to the film? Answer - In no way! They are collaborating for another project which by the way stars Maddy in the lead. Also, Nikhil is not directing it, it is Navdeep Singh of Manorama - Six Feet Under fame.
# Is Shahana a part of that film? Answer - An official announcement is yet awaited.
To summarise, there are two projects starring Madhavan in the lead in fray. While one is called Tanu Weds Manu, is to be directed by Aanand Rai, and is still waiting for a heroine, another doesn't have a title, is pending confirmation w.r.t. its leading lady, is to be directed by Navdeep Singh and is produced by Nikhil Advani and Mukesh Talreja.
Hope this should keep the rumour mongers contained!