This cafe is extremely frustrating. It's a total gong show on the weekends and you'll be very lucky to find a table. The staff can be pretty rude and really I can't blame them because they look so overworked and frazzled.
As for the food - it's not good. Expect frozen chicken, iceberg lettuce, gravies and sauces from dry packages. Basically anything you would think can be microwaved or deep fried quickly. I stick to the poutine when I am absolutely starved for food in High Park and must have something. Anything other than fries or a hot dog and you are asking for trouble. The prices are absurd for what you get. $11 for a club sandwich, $7 for a western, etc..
The reason I say this cafe is frustrating is because High Park is gorgeous and amazing. But why are we stuck with this awful, 1970s truck stop style cafe and cuisine? It's embarrassing for the city. I'm embarrassed to take visitors from out of town here and try to avoid it at all costs. I wish the city would let some food trucks into the park or let someone else take over the lease of the space. I can't believe the Grenadier Cafe still exists with this kind of food, and this service in 21st century Toronto. And in the middle of one of the lovliest spots in the city no less.