I'm not from Canada, I'm from the UK, so I am not familiar with what they use to say Toilet.
However, it depends on how you asked the wait staff. Of course, if you did it politely, he/she had no right to sneer at you.
If the case is that they use a different word to the toilet, then maybe she was offended by it, but I doubt that.
After some research, I found that Canadians (and some north Americans) find phrases similar to "Can you show me where the toilet is?" rude. This seems only to be true for these places. In the UK, it would be fine to say this, we also have a lot of slang for the word "toilet".
I recommend replacing the word with "bathroom"
"ladies’ room / men’s room"
I hope this helps.