My mother-in Law has made that Eagle-based stuff for years- you don't need to pierce the can. That method must have evolved due to folks' failure to keep the boiling water level high enough to cover the can. Which will of course lead to disaster. Any unopened can's contents can be heated/cooked in boiling water so long as the water level isn't permitted to fall below the top of the can.
Here's a link to the "traditional" process, which in my opinion is likely to yield a more consistent result than any method involving pre-piercing/opening the can.