(I don't know how it works in Canada....but for people in the States) If you are in the States, regardless of assess or children (or lack thereof), you should have a living will/medical proxy *at least* (even if you do not have a will for anything else) even if you are married. In many states, when you turn 18, there is no automatic decision over who gets to make decisions if you are too ill (or well, dead) to make them yourself - even if you are married. And there have been some very nasty court cases over who gets those decisions - parents, spouses, or significant others.