Hilarious that this was asked here as I’m currently waiting to hear from Dal but used to work at the DMV.
Basically, it’s a huge grey area. The motor vehicle act says you need to have a Nova Scotia DL but Ontario will expect you to remain there. If you call in and ask, they will definitely say you should but I can say that you will be be totally fine if you leave it in Ontario.
I moved to NS out of prov for my undergrad and didn’t exchange my license until after I graduated.. and so did tons of my friends from ON. Just make sure your insurance knows what’s up - they’re the ones that really matter.