Like most of the European Airlines, the BA lounge doesn't disappoint here in TO. The North American carriers should take note and learn from the amazing lounges from BA and others.
While I find Terminal 3 to be the nicest one at Pearson, having access to the BA lounge has the usual benefits: less crowded than common areas, wi-fi, nice washrooms, computers (for those rare creatures out there who aren't connected somehow), comfortable chairs, magazines and an endless amount of good and drink options. From light snacks to full meals, from water to liquor and passing through many coffee and tea options, there's definitely something here that will please all.
The main dining area is separated from the rest area (where the comfy chairs are) via some tempered glass and you get the feeling of being at a restaurant.
The lounge is on the small side but I've never encountered a problem finding an available seat. You might end up seating next to a stranger but you'll be so happy with all the entertainment, food and drink options that nothing will be able to spoil the experience.