WCF wrapper implementing dispose-finalize pattern
Given that much of the code seems to rely on Service being an IClientChannel, and the name of the class implies as such, it may be worth simply adding IClientChannel to your type constraints and remove all the type conversion code.

Building upon that thought, I notice that IClientChannel extends IChannel, and everything you use seems to be present on IChannel.  You may consider using that interface instead, and renaming your class to reflect that it is not limited to IClientChannel.