Upload & Sell: On
Here's a photo of my TT Airport Commuter with 500L. The pack's not configured for it right now, and so the lens isn't all of the way in, but you can see it's a fine fit.
I don't think you'll have any problems with international flights, although it's quite possible that you'll be asked to check it for short-haul commuter flights (nono of which are probably on this itinerary). I stopped using roller bags (even small ones) a few years ago, and switched to a backpack. Like you, I take two carry on, one is the backpack and the other is my 'personal' or computer bag. It's a shoulder bag much like the one in the link, below. I haven't yet used the TT, but it's no larger than the ordinary day pack that I've used extensively. Even on commuter flights, I've always been able to bring both the backpack and shoulder bag with me, including Canada to UK, GE, US, and AU. I switched from the daypack to TT bag because it was getting too irritating to try to retrieve big gear from the top-loading daypack. Problem solved.
I often have the backpack overweight, but with sufficient margin in the shoulder bag to split the weights. I've never been asked to weigh the gear.
The only time I've travelled with photo gerar under tighter carry on restrictions was a vacation charter flight which had very strict (and well publicized) rules about carry on, max. 5kg. All of the 'main stream' flights seem to be OK with 2x 10kg. OTOH, I've been in Heathrow when there was a security alert, and passengers were limited to one small carry on. Most passengers in the pre-boarding line had at least two carry on bags with them...
Have a great time in Iceland!
MEC bag, http://www.mec.ca/AST/ShopMEC/Packs/LaptopCompatibleBags/PRD~5026-310/mec-carry-all-shoulder-bag.jsp