Hello and thank you in advance for your help. I will be flying to Europe in march and need some advice as to what class to take and how I should book to get the most out of my flight.

Booking Air Canada
March 3, 2014 YWG-YUL/YYZ-FRA
Apr 10, 2014 FCO-FRA/MUC?-YWG

To me it doesn't really matter where I stop as long as I get to my destination. With that being said, I am very tall so I would like to pick my seat ahead of time for the international flights so I can get emergency exit row or something else with more leg room. I also wouldn't mind stopping in the Maple Leaf Lounge before the international flights as well. Currently looking at tango or flex for booking with air canada. Is is worth paying the extra money? Will I gain anything like pre selecting my seat for free ahead of time. From what I have read there isn't really any advantage to booking flex. Thanks