What is the burden of proving the will of a deceased person to his executor?

In Hynes v. Borins, [1972] O.J. No.196, Lacourciere J. held that the burden on the executors is generally discharged by proof of capacity and the fact of execution from which the knowledge of and assent to the contents of the instrument are assumed. The law generally presumes sanity or competent understanding and a will rational on its face and properly executed is presumed to have been made by a competent and capable testator, unless there are circumstances raising well-grounded suspicion that the document does not really express the true will of the deceased.