Try to find out the firm's culture. In Montreal, you could have an Anglophone or Francophone one. A francophone one is likely to be somewhat more stylish and obviously bilingual (a French only outfit is unlikely to be big enough to import middle managers from Europe) and in Montreal, a European style isn't out of place.

I'll echo Romelle that engineers tend to be more casual but for middle management interviews, go formal until you get the job. Then switch . Also, make sure to bring along outerwear suitable for the season. Montreal cools off in the fall and can be quite chilly if you are used to very mild winters.