From the Scirra blog:
[quote:14zerlvi]As promised, Construct 2 projects import to Construct 3...
...So you can rest assured your project will import correctly. (Note if you use third-party addons, you will need to install Construct 3 versions of the addons before importing.)
Hi 
Ashley , — Re third party plugins and compatibility of C2 projects with C3. If I am using Cranberrygame's Cordova plugins in my game (like many other C2 developers who are focused on mobile), it sounds like I won't be able to import that game to C3, with the Cordova plugins in their current state? I will need to rely on Cranberrygame updating his Cordova plugins to make them compatible with C3. Is that the case?
Thanks