Should be okay to carry on but just be prepared to pay for check-in.
My only suggestion is to be very careful on how you pack your bag as in the way you fold your clothes and how you position things. It makes all the difference in how you can maximize every bit of space you have.
I've only been to Paris and Toronto in your list. My only suggestion is to pick up some basic French and grab a map for their Metro system. As for your bag, it looks like an easy target for pick pockets based on where the zippers are located. Put your wallet in your front pockets, not the rear. And watch out for trolls/Gypsies who ask if you speak English at tourist attractions because they might be out to get you.