How to calculate position of a canard?
There are several factors to consider, and depending on your preferences there is not one ideal size and place for a canard. For a first rough concept look at similar designs and use the same canard volume. That is the product of canard area and the distance between its and the wing's neutral points, relative to the aircraft's reference parameters.

$$V_{Canard} = \frac{S_{Canard}}{S_{ref}}\cdot\frac{X_{NP, wing}-X_{NP, Canard}}{l_{ref}}$$

Collect as many canard volumes as you can from different but similar designs and use that for a first draft.

Next, decide on your priorities. Do you want good pitch damping for a pleasant ride even in rough air, use a smaller canard area on a longer lever arm. Damping grows with the square of the canard lever arm while its stabilising effect is only linear. Do the opposite if you prefer more agility.

Next, what center of gravity range do you desire? If, for example, you plan a tandem two seater where due to engine weight and pilot position the second seat is at some distance from the center of pressure, increase canard area accordingly.

So far we looked only at area and lengthwise position. But the vertical position must also be considered. Ideally, the wake of the canard will be above the wing for all practical angles of attack (from cruise to stall), which can be achieved by placing the canard wing high on the fuselage and the wing low. In that position, however, the canard wing might obstruct the pilot's view, so maybe you want to strike a compromise where the wake is below the wing in cruise but above near stall. This can only be achieved with a short lever arm, however.

Regarding the shape: A straight, high-aspect-ratio wing will be best. After all, the canard will fly at the highest lift coefficient of all surfaces so it should have the highest aspect ratio. Use a trapezoidal planform with a ratio of tip chord to root chord of 0.6 - 0.7, or, for simplicity, a rectangular planform which needs only one rig/mold for both sides.

But if what you really want is a good airplane and aren't determined on making it a canard: Place that smaller surface behind the main wing.