• Did you try and retreat?
• How far did the person get in "trying to beat you up" before you deployed the spray -- did they strikes you several times? did they just strike you once? did they only try (and failed) to hit you? did they not even try, but threatened to hit you? or did they simply walk towards you menacingly?
• Is the other person also using a tool to try and harm you? Or are they bare-handed?
• Is the other person larger than you? Smaller than you? By how much?
• Are you frail? injured? elderly?
• Were police nearby? Within earshot?

Courts (and juries, by instruction) often take context into consideration when deciding things like this. Generally speaking, judges in Canada do not like people defending themselves if there were any other option to avoid getting harmed -- and judges have a lot of sway as to the outcome of a trial.