Canards are unusual airplanes.

Let's cover static pitch stability for a moment. Several things have to simultaneously be true during unaccelerated flight:

Summation of vertical forces equals zero;

Summation of moments equals zero;

First Derivative of Pitching Moment with respect to angle of attack must be negative.

In canards, that means that the canard must be loaded more heavily than the main wing. The Wright Brothers figured this out when they were flying from Huffman Prairie, prior to their spectacular demonstrations in New York City and Le Mans.

For safety, the canard must also stall ahead of the main wing, that is, each stage of stall in the canard must precede the same stage in the main wing. This drives you to select stall behaviours in both foils to be similar. Once the loading is higher in the canard, the safety can then be covered.

And despite all of the knowledge gained in Vari-Viggen, Vari-Eze, Long Eze, and Cozy, the Velocity series ended up having to reduce the canard span to allow full range of CG to be used. Rutan Aircraft Factory also ended up reducing the spans of their canards...

I think that it is important to note that even Burt Rutan has abandoned canards. Before he was done with the Catbird (a significant three-surface airplane) he had sawn the starboard canard off entirely. Why not reduce both sides symmetrically? Well, there were antennas in the port side of the canard, but no one knew where, so they only removed canard from the starboard side. And symmetry is over rated anyway - look at the Boomerang, which is the best configuration twin yet.

Anyway, a canard with an engine at each end has its CG pretty far forward, and so, the canard that was about right would be pretty large...

Billski