I've had many problems connecting to a YYZ transborder flight over the years. If the inbound flight is delayed on the tarmac or the luggage claim is slow (and it often is), you can easily spend the first 45 minutes of your connection before you even get to customs. This is something that YYZ-based posters often don't understand.

Starting in YYZ is not that bad. Even on a Friday afternoon, you shouldn't need more than 45 minutes to get through the customs and security line-ups (and that's being generous). Arrive 90 minutes early and you'll have time to check-in and stroll to your gate before the plane starts to board.