Don- Look at I don't know anything about Canadian art festivals, but Zapp is probably the most used in the States. It will give you the submission requirements, so you'll be able to offer your clients images ready to submit. You'll also need to have them set up their booths, showing the work as it will be displayed (well... not actually how it will look at the festival, but cleaner, and less cluttered.)

Another juried service is

Another good source of information is He has a good track record of supplying images which get artists into shows, and his blog has some good info.

I'm not sure the image you posted will do the trick. The artwork needs to "pop". Jurors have only a few seconds to view the artwork (usually projected), and it needs to catch their eyes quickly. I'd suggest trying the same subject with different backgrounds- gray and black. Also, if the small sphere is a separate piece, don't include it in the photo.