Though clearly he didn’t start using the phrase until a few years after it was invented, the WWF’s Stone Cold Steve Austin frequently threatened to open a can of whoop-ass on people.
And then usually proceeded to do so.
This led to a hilarious moment during a segment with Booker T in which the two of them were fighting in a supermarket. Booker briefly lost sight of Austin, and then heard the opening of a beer can directly behind him. Cue a hilarious wide-eyed look of horror as only Booker T could have pulled off.
I know for an absolute fact that it predates Uncommon Valor. My first job out of high school I worked with a guy that said it all the time. That was in July of 1979. He used the phrase when he was describing a boxing match he saw on TV.
If you look at the entomology of most languages, grammar usually involves shortening of longer phrases because people are lazy:
I am -> I’m
The stars that are shining… -> the shining stars
So, the phrase “whup ass” is most likely a shortening of the common expression “…will whup his/her/their ass.” The “can” part is likely to be a way to express intensity or pluralize it. Again, the theory of lazy grammar states that “can of whup ass” will more likely be used that “a six pack of whupass” or “a dozen extra large grade A helpings of whupass” or “a spoonful of whupass” (Will and Grace.)
So, while the origin of the phrase could have been done randomly at any time “whup” first met “ass,” it wasn’t popularized until “Stone Cold” Steve Austin used it as a catch phrase and started selling t-shirts with that on it, thus standardizing the plural/intense form.
Edit: “Intense form” usually is the more/most/-er/-est forms, although “he has the potential to be the wuppiest whupass whupasser there ever was” does deserve to enter the language.
Uncommon Valor was out in 1983. I first heard “open up a can of whoop ass” from a guy I worked with. The first story he ever told me, about a boxing match he watched, was in June of 1979. I have no clue where he heard it from. I’ve never heard anybody claim an earlier time.