I haven't been over to T3 for years, so I couldn't tell you what dining options there are there.[/QUOTE]

Dining is fine in YYZ, nothing spectacular but ok. Lounge is upstairs between gates 33 and 35 i remember. 3 hrs is certainly enough.
Yes you need to collect and recheck and redo security, but T3 is usually a doddle!
Look out for the nice BA lady with the scottish accent at T3 , she is really helpful.
And although people in Montreal may argue otherwise, they can handle winter in YYZ