American Airlines flies between: Toronto - London, Toronto - New York, Toronto - Miami, Vancouver - London, Toronto - Chicago, Toronto - Los Angeles, Calgary - London, Vancouver - Los Angeles, Montreal - Miami, Montreal - London, Toronto - Boston, Montreal - New York, Toronto - Dallas, London - Toronto, New York - London, New York - Toronto, Montreal - Chicago, Los Angeles - Sydney, London - Vancouver, London - Calgary, as well as several other routes.
If you're flying on American, you'll almost certainly have to pay for any checked baggage. Your first checked bag will run you $25 USD and a second will cost $35. Standard weight restrictions apply on AA, with the maximum weight being 50 pounds. Note that if your bags are overweight, you should expect to pay a minimum of $100 USD. American Airlines allows two carry-on items with the usual restrictions, with one being a personal item that is generally considered to be a relatively small item such as a purse or laptop bag.