A couple of weeks ago, I saw a tweet and noticed on flightradar that the Saint John to Montreal Air Canada flight was diverted to stay in Canadian airspace, because as of Jan 1, the US requires all aircraft in US airspace to be equipped with ADS-B.
All the other flights from the maritimes to Montreal and Toronto have continued the normal routing across Maine, so I assume that only the odd Dash 8 in the AC (Jazz, technically) isn't equipped with ADS-B. Last night, I was coming home from Montreal, and when the Montreal to Moncton flight was just about to board, they announced that it was moving to a new gate and would be delayed by 20 minutes, and the crew and all the passengers hustled off to the other gate. Then they announced that the flight to Toronto City that was scheduled to leave from the other gate would be moving to the gate that the Moncton flight was scheduled to fly out of originally.
The aircraft didn't move, so that means the Dash 8 that was scheduled to go to Moncton was now going to Toronto City, and the one that had been scheduled to Toronto City was now going to Moncton.
I wonder if it's for the same reason? How many of Air Canada's Dash 8s don't have ADS-B? Bored travellers wonder about this stuff.