In Canada, for the most part, there is little day-to-day difference between couples who are legally married and couples who are common law. You can get benefits at work, get a family membership at the gym, and generally live as if you are married. One significant difference, however, is in matters of estates law.
If you are not legally married, you are entitled to nothing from your spouse’s estate unless you are legally married or you have signed wills. Truly: nothing. You have no inheritance rights unless you are dependent on your spouse, in which case you have to sue your spouse’s estate to receive anything. (And even then you will not get the full estate, only what you would have been entitled to if you had separated the day before your partner’s death).
Common-law couples are a group who truly need to have estate planning documents in place. Society may not care whether you have walked down an aisle, but the Ontario government certainly does.