Original itinerary was Louisville to Halifax, Nova Scotia and return July 1-9, 2016. Coming back I had to fly through Toronto. I had a 2 hr. 26 min. connect time in Toronto. Without notifying us, AA cancelled the connecting flight to CLT and put us on a flight that gave us 20 minutes connecting time in Toronto. Toronto requires at least an hour and half connect (among other things you have to go through customs). The 20 minute connect was impossible to make and in fact not a legal connecting time!
We had to stay overnight in Toronto. Very lucky to find a hotel. With cab fare, hotel, etc., this cost us about $400.00. After some wrangling, AA in Toronto said they'd give us a $200.00 voucher to help with the hotel if I called them when I got back in the States. I've done this and also emailed them. No response. We were lucky to get home at all, as everything was booked on the 9th and 10th.
A year ago, when flying to Central America, AA cancelled our 2:00 PM flight and put us on a 6:00 AM flight, again without telling us. Delta, by contrast, notifies us if there is even a five-minute change on a flight.
Beware of AA. This used to be a good airline. Now I can't imagine a worse airline.