Actually the only missile that France usually sells with its conventional subs (&also to the Pakis) is the exocet anti-ship missile-which is much in the same class as the harpoon ,though significantly less range(about 50kms).
The Exocet has not been designed to be fitted with a nuke warhead&even if the Pakis try to do something-the warhead size of the Exocet(bout 150kilos) makes fitting a nuclear warhead rather impossible technically.The French sea launched land-attack cruise missile (Scalp Navale) which is pretty much in the same class as the American JASSM ,won't come out till 2008&cannot be exported without EU consent.Other than that the only other sea launched missile they have now are their SLBMs!!!
Moreover now France seems to be wanting to do away with its arms relations with Pakistan-It is close to signing contracts to sell India 120 Mirage 2005 fighter bombers,6 Scorpene subs(next gen variant of the one ,the PN operates)&loads of other smaller contracts.Doesnt make sense to continue sticking to a semi-failed Islamic state.