The way I like to think about work is as if you're giving (or taking) energy from a system. You're not transferring any energy into the system: the object is not changing its kinetic energy nor its potential energy, etc, so your work is indeed zero. You are definitely using energy to attempt to...
Remember that the mass and radius are not determining factors when it comes to speed. Meaning cans of identical geometry but different masses will effectively have the same speed through the descent. The more hollow it is, the slower it will go due to having a higher rotational inertia, meaning...