When the sinks are supported by the plywood, how will you ever remove it without removing the stone? Sawing underneath the counter sounds really unsafe! I understand that it's unlikely that you'd want to but such an installation would not be my choice.

What if there's water infiltration and it starts to rot the plywood?

The Julien site shows installation methods and sandwiching it between plywood and countertop isn't one of them. The fabrication should have included the brass inserts embedded in the stone, or something similar. I like the idea of a sink strap/harness because the upward pressure insures better contact with the countertop. Though it isn't "necessary", it's a good idea.

http://www.prochef.ca/en/installation/

I am only commenting to bump this up for Joseph to see. You must be so excited to see your kitchen coming together. I can't wait to see the pictures. Your plans all sound so lovely.

I'm not a fan of the plywood method. Plywood cannot push sinks upward constantly; straps can. Abandon the plywood and strap the sink, please. If you ever need to change it, you'll be glad you did.