What she said. We've never been able to do it direct, and I've only seen those flights in the high season.
If you can't get a direct flight and have a choice of how you make the connection, try getting one of the US carriers direct to Newark or something like that, then the connection to Orlando. Then you can pre-clear customs in Halifax, and the prices are usually lower, even if it's a codeshare. (The US carriers charge lower taxes and fees generally, besides having slightly lower prices for similar routings.)
Good luck.