Except that its illegal to use a firearm for anything other than hunting and target shooting in Canada. Even if its in self defense, your looking at assault with a deadly weapon, attempted murder, manslaughter or murder charges
That's not quite right. "For self defense" is not a legitimate reason for owning a firearm in Canada, but there is nothing in the criminal code that states that specifically prohibits the use of a firearm when a different type of deadly force would be legal.
Oh...and by the way...it is also legal to posess a firearm for pest control, predator control, or wild animal defense (bears and cougars) in Canada. Certain people who work alone in the wilderness and cannot carry a long gun due to the nature of their work can actually get an ATC (authorization to carry) for a pistol to defend themselves from animals.
This sure isn't the USA, and we DEFINITELY don't have any sort of castle doctrine. If you shoot an unarmed burglar, you're going to jail. If you shoot a burglar that has a pistol in his pocket but has not threatened you directly, you are going to jail. If the Crown Prosecutor believes that you intended to kill an intruder just because he broke into your house, you're going to jail.
But...
If you shoot an intruder that has given you reasonable cause to believe that he (or they) intends to do grevious bodily harm to you and/or a family member and is able to do so in the immediate future, you will probably still get cuffed...but you probably won't get convicted. There are lots of conditions and "yabuts" and "except when" clauses attached to that...but the bottom line is that if a "reasonable person" would have had cause to believe that the intruder intended to kill someone in the house and had the means to accomplish that, then an equivalent level of force may be legally used in immediate defense of life. Once the deadly force threshold has been crossed (be it a knife or a gun), then deadly force can legitimately be used in self defense.
In a case like Tinkerer's where the individual has already attacked an immediate family member using deadly force on one occasion, you would have a hard time finding a Crown Attorney who was masochistic enough to want to press charges.