The canard surface must be able to force the main wing into an angle of attack close to stall, in order to obtain minimum stall speed. To accomplish this, the canard must develop a much higher peak lift coefficient than the main wing, or the CG must be far enough aft to prevent the canard surface entering deep stall before the main wing develops close to its maximum lift. I have weighed the pros and cons of the canard versus tractor layout, and it came down to pretty much a draw. The portion of the main wing that is influenced by the downwash from the canard tail will have a lower effective angle of attack, and thus develop less lift than it would in a conventional tractor layout, and the tip portion of the main wing, which is outside of the canard tail downwash, will tend to have a higher effective angle of attack. This will tend to cause tip stall of the main wing at a lower average lift coefficient than would be the case with a tractor layout. In any case, in the full-scale world, stall/spin accidents appear to be about as common with canards as with conventional airplanes.

In most tractor layouts, the horizontal tail contributes to lift, unless the CG is at or forward of the wing aerodynamic center, although the contribution is not usually more than a few percent, due to the large downwash acting on the horizontal tail.

Pusher prop canards also suffer more from torque reaction than do tractor layouts, since they have no flow-straightening surface behind the propeller. Hovering without torque rolling would probably be impossible with an aft-mounted pusher prop.

Early aviators (with the notable exception of the Wrights) pretty much settled for the tractor layout, since it placed the center of lift well forward, permitting the engine to be at the nose, not behind the pilot, where it would present a clear hazard in a crash. I did a lot of design work on a canard pattern model, but never built it, when I reflected on what would happen in even a mild crash, when all that rearward mass forced itself up forward, tending to clobber everything in its path.