I don't know if Hannibal merits a special trip from Canada, but if
you're going to be anywhere within a day's drive it's certainly worth
the detour.  A lot of the outlying stuff is tourist-tacky, what you'd
expect: the Huck Finn motel, Twain-motif gas stations, and so on.  But
the central area around the Clemens home is impressive because of how
little it has changed since the 19th century.  In large part, of course,
this reflects the hard times Hannibal fell upon in the 20th
century--nobody had the money to do much rebuilding.

One strong suggestion I'd have is to take the time to do some
off-the-track hiking, up through the woods to where you have views of
the Mississippi from the bluffs (just keep an eye out for NO TRESPASSING
signs; there's lots of public or unsigned area, though).  More than
anything else, I think, this gave me the feel for how the terrain works
in all the descriptions set around town.  You have to get to where you
lose sight of automobiles & then the magic begins to work.

David Sewell