In Canada, what form is needed for a spouse to make heath care decisions?

In Ontario, Canada what form or document does a spouse have to sign so that she may make the decision to end life support for her husband? He is on life support, is about to lose his leg, has had a massive heart attack,and his kidneys are not functioning. She would like to end his suffering as he had requested of her when they discussed this issue in the past. He does not have any kind of directive.