I was hoping to see a fellow Canadian in this thread! Thank you for the link on the legal differences. I'd also add, culturally speaking, there are many different meanings the word "sorry" can have...
There's the sincere, "Sorry!" which has a slight rise at the end and is said quickly. That's what you say when you (gently) brush into someone, or cut them off walking.
The even quicker spoken, "Sorry!" which is an expression of surprise or startlement. This is what you say to the lamppost when you've walked into it.
The, "Oh God, I'm SO sorry! Are you okay?" For times when you've mowed someone down with your shopping cart or let your baby spit up on them.
The eyeroll combined with an annoyed, "So--orry!" if you think they're overreacting or being ridiculous.
The questioning, "Sorry?" when you're confused and need someone to explain what they've just said. It basically means the same as, "Wut?"
The "Sorry-sorry!" if you've just embarrassed yourself. Dropping the toast butter side down is a good time to use this one. It's not directed at anyone or anything.
The empathic, "I'm so sorry!" which just means, "I feel sorry for you."
And the purely passive-aggressive, flat-toned, "Sorry if I've upset you." Which usually leads to the other person hollering, "No, you're NOT!"
Yes, in Canada, "Sorry" can even be the equivalent of putting a middle finger up, depending on how it's said.
For the record, I apologize a lot.