I fly in and out of Toronto frequently, so here is my advice:

You are allowed 1 carryon item that is from a specific list posted on the Pearson Airport website (purse, computer). This makes the check-in line very long and tedious, but since there is rarely anyone in the "First/Medallion" line, you avoid most of that headache.

The initial customs line can be brutally long, but that process has not changed due to the new screening rules. As a result, the first security checkpoint wait is no longer than it used to be.

The change is that they have second screening checkpoint before the gates where TSA goes through your carryon in painstaking detail. However, the past 2 times I was told to "go around" and was somehow exempted from this secondary process. No clue why.

My advice is to book the first flight out in the morning. Customs opens at 4:30 AM - get through as quickly as possible and just relax on the other side.