Your first choice should be the check-in desk at the airport where you board the flight TO Toronto.
These days, airlines that interline at all usually interline enough to be able to print boarding passes for connecting flights, so chances are excellent that Delta will be able to print a boarding pass for Azores. (This all assumes both flights are on a single booking, of course).
If you're pressed for time at your departure airport, or Delta can't print a boarding pass for you, you get a second chance at the Azores check-in desk or kiosk at Toronto.
You don't tell us where you're coming from, but all Delta's flights to Toronto originate in the US. Like most North American airports, Toronto Pearson does not have an international transit area, so as an arriving passenger on an international flight, you will need to pass through Canadian immigration, and then end up landside. On your way to the departures security check you can go to the Azores check-in desks and get your boarding card printed.
(Note, though, phoog's experience in comments below, which partly contradicts this. However, you can still generally expect that if an airport provides a separate path for transfer passengers, then there will also be a transfer desk where you can have your boarding pass issued somewhere on that path, if you need a boarding pass to reach the departure gate -- or you can get it at the gate otherwise. You'll want to ask the Delta cabin crew for advice on your way to Toronto if you don't have the boarding card by then).
According to Wikipedia, both Delta and Azores use terminal 3 at Toronto.