In Ontario, there is no such thing as a legal separation. A separation is a matter of fact: you are either living together or you are not.
While some couples may choose to live in the same home while considering themselves separated, the courts consider a number of factors to decide if this is indeed true. Factors include, doing household chores such as laundry, cooking, or cleaning for each other, spending time together with family and friends, celebrating special occasions together as well as sleeping in the same bed and/or having a sexual relationship with one another.
Perhaps the best way to gauge if you are separated is to ask your partner and those people closest to you whether or not it is clearly understood by them that you have separated. If this is unclear to your partner and/or those closest to you, then it may not be clear to the courts.
Noting the date of your separation is very important, as this will mark the date when your property rights come into effect.