Montreal's a big city.  I've been to restaurant where I was 100% certain not to meet anybody I knew only to end-up sitting few tables from them.  Often I also went to places where I expected to meet my entire family and friends but didn't see anybody I knew.  It's the draw of Lady Luck.  Each time you go in public, with a lady you don't want to be seen with, you take a chance.  
Don't forget, friends of the ones you're hiding from might also see you!
Better don't pay attention and think of an excuse beforehand.  Could be a customer?  A business associate maybe?  Or a friend you haven't seen in a while?  Of course, excuses like this are mute if you are all over her when you're spotted.
Be careful! 
