Honestly, I've never had a pair of canvas shoes with good enough arch supports that I could wear them all day on concrete without aching shins by the end of the day. Maybe if you found the best ones you could and added some type of Dr Scholl's (sp?) product you'd have better results.
If you have a moral issue against leather, how do you feel about artificial materials? There are a lot of good hiking sandals made without any animal products. They usually have nylon and other things that aren't natural, but they aren't leather.
I always suggest to anyone that you take 2 different pairs of shoes, 2 different brands, and rotate them each day. The longer you wear the same pair, the more likely you'll get hot spots on your feet.