Place two fiber prints face to face after removing all excess moisture. Put them between two pieces of blotter paper (the ones used for desks are ok if they are white). Put a big book over the sandwich and allow the prints to dry. When dry, undo every thing and the prints will fall apart very straight.

Another option is to get an electric print dryer off ebay and use it--on low. If the canvas looks soiled or chemistry stained, first wash the canvas in warm water (not hot, it will shrink) and mild detergent. Let it air dry.