In Ontario, section 6 of the Succession Law Reform Act states that "A testator may make a valid will wholly by his or her own handwriting and signature, without formality, and without the presence, attestation or signature of a witness." A will created pursuant to these provisions is known as a holographic will; a holographic will is a will that is entirely in handwriting of the testator. It does not have to meet the formal requirements regarding execution that a traditional will does.
So long as the will is intended to dispose of the testator's estate, is entirely in the handwriting of the testator, is signed and dated by the testator the holographic will can be held to be the Last Will and Testament of the deceased.
Now, just because you can do something that is no reason to do it. You can make a holograph will but it's best not to do so. A carefully professionally written will is not very expensive and is better protection than a holograph will. But in an emergency a holographic will works.