It depends on who you book the tickets with? If you book it with TG, you can check it at
www.checkmytrip.net. If you book thru TA, then you will need to check with your agent on what system that they are using. For example, if they are using Abacus system, you will need to check at Abacus website at
www.virtuallythere.com
You can prebook your seats either via your TA or through your local TG office.
Enjoy your flight!