What route are you taking with which carriers? In many cases you will have to collect and drop your bag again and clear immigration into Canada if not into the US as well if that’s your final stop. You may even need to change terminal which means you are definitely heading landside.

So the 5.5h layover may be much less. There isn’t much airside aside from lounges most if not all are closed for a large chunk of that time as YYZ has limited scheduled flights between 1 and 5 - which lounge depends on which area you clear into (domestic/transborder or international).