its much more seemless, now. Assuming you are doing the transit with all *A (or other carriers within T1), you just go through a cursory customs check and get deposited into the international departures area. I've never seen a line there, except in bad IRROPS - you just follow the signs to 'Customs B' - if you've gone down an escalator before you've hit the booth - you've gone too far. You do have to fill out a customs form, and I don't think this works if for some reason you can't get your BP printed before you arrive at YYZ. Bgaggage is transferred automatically.

Note that if you are arriving late night - that area may be closed - not sure whay time it closes - just from my anecdotal passing by, it is still open at 9:00pm, but not at 11 pm. Also note that you'll still need to meet all Canada entry requirements - so if your passport is from a country where a transit visa is required, IIrC, you'll still need to get that.

As as long as you can go through that process, you shouldn't need much extra connecting time. I actually haven't done it, as mostly I'm ending my travel at YYZ, but I'd say 4 hours is more than you'll need - Is say 2 hours would be more than enough time.