That's because it's Luton. One of the moderators here on FT is called LTN Phobia for a reason.
There are plenty of airports where spending the "night" (depending on your body clock time) ranges from reasonably pleasant to bearable, though I don't know about YYZ.
At least Luton doesn’t blast you with announcements... Though it’s been a while I admit.
To be honest I rarely sit around YYZ outside the lounges, which aren’t great but beat the gates. When they’re open.
It should be reasonably quiet at these hours though, and I believe some of the food places are 24/7. And there should be tons of spare seating as well. Find a deserted gate but to be honest if you take it easy getting through immigration you’ll only have about 2h in my opinion before you can head to US pre clearance.