I strap the cans to the wall/cabinet with bungee cords.

Bitter Apple from pet store.  But instead of having to spray your
wastebaskets constantly, I would just go and buy some that have a lid on them.

On Fri 12 May 2006 05:29:51a, Thus Spake Zarathustra, or was it Unknown
One?

Get some "bitter apple" spray.  It smells nice and cats hate it (they don't
like the smell that much and the hate the taste).  Most pet shops carry it,
and it's perfectly safe.

If it were my cat doing that; I would go to the local toy store and
pick up a plastic squirt gun.  When the cat knocks over the trash can I
would squirt him with it.  The next time the cat goes for the trash can
I would pick up the squirt gun and the cat would see it and run and
hide.  After a short while the cat would realize the knocking over the
trash cans behavior would no longer be tolerated.  You would usually
only have to spray the cat one time; they quickly figure out that being
sprayed by water is not a lot of fun.  I don't think the punishment is
overly cruel, I've never had to use it on my cats more than one time;
cat's don't like water but it's not like I'm spraying them with hot oil
or something.