Try Westjet. I checked fares from St. John's to Halifax and there are pretty low seat sales, less than $100. You have to pick the right dates.
Not always the case, sometimes I feel like WS is working side to side with AC or ripping people off. most of the time, their fare is within $50 less than AC. They drove Jetsgo out of business, and now both have a monopoly over the market.
Nextime, I'm flying TPA-YYZ, I prefer connecting in DTW or EWR than going nonstop. Hopefully, I won't have to wait for my bag to arrive 45-60 minutes at YYZ. Last time AC did that to me, it took about an hour and a half to get our bags out. That day was a mess, and everyone was angry at AC. YYZ is a failure in my opinion.