There is one included, KLM lounge that they use for the 1:40 a.m. flight. If you have 10 hours and it is the 1:40 flight then why don't you take the flight earlier in the day? It isn't more than 10 hours earlier IIRC.
I would not spend 10 hours in that lounge and it may not even be open - it is used for KLM and a few others and the CX flight and opens for them, and I think most are in the evening. So I bet it is closed in the daytime as is the CX checkin other than for the 2 flights.
There is a paid lounge called Plaza Premium for $27 or so (look for discount coupons online) also in T3. That one is actually nicer than the KLM lounge. Free with Platinum Amex, as well.
For this layover other than trying for the other flight I'd go into Toronto for a while, of course I live here so I can do that rather easily.