Well, they fall off of ships all the time, especially in rough weather (all the time is hyperbole, but it absolutely happens). So sure, you can probably push one off with a pretty big lever, but shipping containers are actually designed to "clip" together to an extent, to make the load more solid. Problem is, the canal is only about 24 metres deep, so you're going to end up blocking the canal with containers instead if you just push them off.
The modern shipping world is all about containers, container cranes, and container ships. 99 Percent Invisible hosted some episodes of the Containers podcast [0] that will probably provide some insight.
Is it common at all to get containers off a ship outside of docking areas?