If it's a Canada to intra-European transfer (e.g., YYZ-FRA-CDG), 1.5-2 hrs is more than fine (unless you're flying AC to CDG and then *A, then it's 3-3.5 for me).
If I have an onward international connection on a flight I really wanted, then I'd book something that had 3 hrs at the minimum. For example, YYZ-FRA-BKK.
Regardless, you'll be protected on the next flight, or if customer service is really good, they'll be proactive and offer something earlier, if available. The only caveat is that you might not get the seat you want or had reserved.