It all depends on the winds of course (and which of the parallel runways KLM uses), but here's how to get to good spots for the approach to runway 23 and the 24s - these are the most commonly used rwys. I believe that this flight is more likely to use runway 23, but someone who is at YYZ
more often would be able to say more accurately.
RWY 23: It's about a 20 min walk from terminal 3, or served by TTC bus 58 (westbound, extra fare applies) or Mississauga bus 7 (also westbound from the airport). There is a Wendy's with picnic tables behind it, (B on the link above) right under the runway 23 approach. To get there by foot, turn left after you walk out of the arrivals level of T3
, and follow the sidewalk all the way to the lights (airport rd). Turn left here, and walk ~15 min till you see Wendy's on the right.
Later in the evening, you can go to the back of a parking lot a little further from the runway (spot C on the link above) which gives some good side-on approach shots.
RWY 24R (24L is rarely used for summer arrivals): The typical spot is the Arizona's parking lot on Carlingview (B in the link above). It's half hour by foot, just turn right at the Airport Rd lights when you're leaving the terminal, and right again at Carlingview (3rd lights I believe). You can explore other spots along Carlingview as well. By bus, it's the same two as before, just take them eastbound and get off at Carlingview.
Hope this helps!