I'm travelling from Pearson airport (YYZ) in Toronto to the US with a TN Visa application, which I'll need to bring to the "US port of entry." Will that be at my destination in the US, or does it happen right at Pearson? I know that other US customs/immigration activities happen at Pearson, before you ever leave Canada, so I'm not sure if this does too.
I ask because I need to plan how early to be at the airport: 2 hours for security, or 4 ours for security + immigration?