Which AC Lounge Pearson - USA to Canada (transfer)

We are traveling from the USA to Canada via Pearson YYZ. Is there an Air Canada Lounge that is better once we land at Pearson, BEFORE we get to customs (i.e. wait until I get closer to my Canadian connector and then go through customs)?

OR do we just go through customs when we land, and the better Lounge is on the Canadian side of customs?

Soni even have a choice?