Azrael said:
I think what's canonical and not canonical is the work of years, not lists or even mainstream critics. Has a lot to do with what gets taught, and therefore the academy, rather than a popular audience.
That is certainly true, especially with American lit where you have a guy like Melville who kills his own career by writing Moby deck (to the point he was begging Nathanial Hawthorne to ask his old college buddy the President for a government job) and yet 80 years later it was regarded as one of the greatest novels ever.
The bigger problem with the American cannon is that it was put together by Ivy League professors in the late 19th century who primarily looked at fellow New Englanders with Twain sneaking in there on the strength of living in Connecticut at the time. In the 20th century that view has been expanded by Midwesterners like Fitzgerald and Hemmingway, but prior to 1900, who are the great American writers from outside the Northeast?