I also think you are cutting it too close. I have crossed through 4 different Canadian/US Crossings. As others mentioned, getting back in to the States takes FOREVER...and Im an American.
I guess the bigger question you need to ask yourself by trying to make an early afternoon flight..."what will we do if we miss our flight?" If you have status and booked a better category, you may be able to get on the next flight...if you book a cheap category, you may be out a $200 change fee per ticket or the tickets may be forfeited completely and you will have to buy new tickets. Also, will your tickets be covered on your
travel insurance if you do miss your flight?
And the
travel agent in me says...be aware that the airlines CAN change departure times...typically up to 90 minutes (earlier or later) without having to compensate you or put you on a different flight...and since airlines say to be there two hours early...it covers their tail when they make the change. You simply need to get your butt on that flight and there is nothing you can do about it unless you pay for a different flight. Occasionally, an airline will work with you...but sometimes they will not. We have status on Delta and they changed our flights on Thanksgiving day...it extended our layover by 3, so a 7 hour layover in Atlanta on THANKSGIVING...we left 90 minutes early...and then layover and then left 90 minutes late. We got a few days notice and that was it. I was pissed...I have an IATA and status and there was nothing they could do for me. They even oversold the flights...and well, you know how that can go.