you have specific route and airport requirements. The answer is - you search YYZ-ARN or ARN-YYZ for June and July and see what's available. That's your answer. There is no "which ones to try" - if any are available, they'll show up. If they're not, they won't.

That said, you're kind of in the no-man's land of partner J bookings right now. Most seats are booked 12 months out, and then partners may make some more seats available 1 month before departure all the way up until departure.