I looked up common law marriage in Canada. It is very complex, as it depends on the laws of individual provinces. I won't go into it further, as it heads off into legal territory, but I did find that, in general, if a common law marriage is recognized, the surviving common law spouse does not have the same inheritance rights as a legally married spouse.
It is also possible that a caretaker could argue that he/she had an oral contract with the deceased. There was a famous US case that begat the word "palimony" because a live-in partner sued for the kind of settlement that a divorced spouse would get.