Canon is a pattern of established information concerning fiction. It establishes what stuff is real and what stuff is baloney. To say that a piece of information is non-canonical means that said information should not be held as trustworthy, especially if it conflicts established facts.

Concerning Animaniacs

It is difficult to establish what is and is not canon in the Animani-verse. There are several origin stories for the Warners themselves. And none of them could EVER explain how they were created in the 1930's and yet appear BEFORE that timeframe in numerous cartoons. Pinky and the Brain presents similar problems.

The best rule of thumb may be to treat each individual segment as an alternate universe, based on a more consistent universe. For instance, the Warners are almost always treated as siblings, even in Star Warners. Their connection to such things as Ralph, the water tower, and of course Warner Bros. itself cannot be disputed. However, all the characters exist in the same "universe", being able to make cameos and on rare occasions even directly communicate with each other in several shorts. They also share the universe with the cast of Tiny Toon Adventures and the original Looney Tunes characters, since multiple cameos from both series are present.

Since the show specializes in madcap antics, and often breaks the fourth wall, it may be almost impossible to establish "canon". Keep in mind, the show's writers created the "Please Please Please Get A Life Foundation".