"The Finance Department of Canada estimates that melting down the metal from the pennies and reselling it in the industrial sector will bring in $42.5 million in revenue."
So, they're going to buy $310m worth of pennies, melt them down, and sell them for $42.5m? That doesn't seem like a worthwhile exercise.
Is that what you mean?
It's the same as when you give change to a stranger on the street - exchange two fives for a ten, and you're no better or worse off financially. You haven't bought anything, just exchanged for a more convenient set of tokens.
Also, by buying them back from the banks it's the government that takes the hit for the cost of de-circulating the penny, rather than the banks or the consumer. If private industry were taking the hit, people would fight tooth and nail against retiring the penny.
(If the scrap value were higher than the face value, presumably the private sector would take the pennies out of circulation, and no government action would be required.)
When you return a cent coin to the central bank, you are simply depositing money in your account with the central bank - you give them one cent of cash, they give you one cent of account balance - and taking deposits does not somehow cost the bank the money that they take as a deposit. Now, the central bank is in the special position that it can create coins and bank notes, which is why they don't necessarily lose any money when they melt down the coin you gave them, as they can just mint a new one, presumably a cheaper one, and the amount of money they have won't change, except by the difference between the scrap value of the old coin and the cost of producing the new coin.
It would be a pretty poor currency user experience.