Odd though it sounds since you have a symetrical airfoil on the main wing you would be best off by selecting a CG location that results in a fairly low stability margin. The less work the canard has to do the better.

Also if you make a new one may I suggest using a "proper" airfoil? Since the rear wing is symetrical by the looks of it I'd suggest a Selig 8020 airfoil. He designed it as a stabilator airfoil for gliders to operate at fairly low reynolds numbers and have low drag for modest angles of attack. It's also more stall resistant than many other options.