Would canned pineapple juices be as effective a tenderizing agent?

No, they would not. Fresh pineapple or pineapple juice is typically used as a tenderizing agent because it contains bromelain, an enzyme that breaks down proteins. Canned pineapple juice, on the other hand, has been heat-treated, which destroys the bromelain enzyme. Therefore, it would not be as effective in tenderizing meat.