I have some recent experience with a large canard airplane, and found that, regardless of the formula you use, the fact is that it really depends on the lifting potential of the canard.
In the case of the plane I worked on, I found that what "should have" worked didn't... By increasing the span of the canard, switching airfoils, (to an Eppler 197) and increasng the proportion of elevator to canard. (elevator was about 30% of the canard chord) everything worked great. (Andy Lennon's book, "The Basics of RC Model Aircraft Design", available through Model Airplane News, helps a lot.) I found that if the canard chord drops below about 5 inches, you may as well use sheet balsa, as opposed to an airfoil. (Reynolds effect, especially at lower airspeed)
One bit of good news...
Since canard aircraft generally have a wider safe CG range than conventional aircraft, you might find that simply moving the CG a bit aft will help a lot.
When they're right, they're fun!