Halifax has some great theatre and Symphony Nova Scotia is based here as well. The jewel in the theatre crown is Neptune theatre. Every year they have a half dozen plays from October to May/June and some summer productions in the Dumaurier studio theatre as well. They have a wide range from Canadian playwriters to musicals such as Grease and Les Miserables.
Then there's the summer outdoor company Shakespeare By The Sea. This amazing company is 10 years old and has been bringing their own spin on Shakespeare to the people in Point Pleasant Park. They are simply fabulous! http://www.shakespearebythesea.ca/ There are also lots of smaller rep companies in the area with excellent smaller productions.
Halifax's Symphony Nova Scotia is a tight well run and very popular symphony that also brings classical, big band, Broadway and lots of other kinds of music to us. Even ballet as they have backed many other kinds of popular arts and artists such as the Nova Scotia Mass Choir.
Dress Code: Generally, Neptune goers dress smartly but there's no code as such. For an outdoor helping of Shakespeare, bring a jacket in case the evening is cool or damp as is very possible here in Halifax.
Check out what's playing. There really isn't a bad seat in the house and there is always a 'pay what you can' night where you contribute what you can afford or bring non-perishables for the local food bank....all proceeds to them.
Dress Code: It's not overly dressy either (as most nice theatres here in the U.S. are) so go in whatever you'd wear to someone's house for a nice dinner and you'll be fine.