Why not use something that was intended for cleaning leather if you've got leather shoes? How about plain old saddle soap? And incidentally, the handcleaners available under various names today were originally developed during WWII as fabric preservative, specifically, for silk - remember parachutes used to be made of silk. It should work just fine for cleaning canvas shoes without destroying the fabric. Just be careful of the stiching on the outsole, it could dissolve the shoemaker's pitch used to hold the thread together.
Mel[/i]