I don't know of any frameworks off the top of my head, but I can infer some of the answers based on experience in other platforms. And those answers are not very promising, unfortunately.
1) If you want your app to be cross-platform, you need to design it as such from inception. Otherwise you're in for a lot of work no matter how you slice it.
2) Because WP and Android use different languages for native apps, you have a big problem in just getting your source code targeted to both platforms. If your codebase is already in Java, you'll need a Java -> C#/VB/C++ translator to make it work. I'm not sure that a product like that exists. If you had started with, say, C#, you could utilize something like Xamarin to target Android and WP at the same time, but like I said I'm not aware of anything similar for Java->C#.
3) If your app is written in HTML 5, then you could adapt it to work on WP8 with very little extra effort. But in that case I bet you would have already known that you're cross-platform-compatible and wouldn't ask this question to begin with.
4) If you're resigned to rewriting your app while maintaining its core design the same, then the basic methodology is as follows:
a) refactor your app into well-defined, loosely coupled components.
b) factor away all Android specific APIs into adapter classes and have all "core" functionality written in terms of those adapters
c) port your core classes to a different platform (WP) in a WP-supported language, such as C#. This would be a straight, mechanical but nevertheless manual rewrite.
d) reimplement your missing adapters on WP to take advantage of WP APIs, while leaving internal-facing interfaces the same, so your core classes just work.
e) all of this makes sense only if there is enough complex core functionality to warrant the rearchitecture + translation. If your app is little more than glue shuffling data between external data sources, then all of this is not worth it, and a compete rewrite is the only way to go (sorry I don't have a QR reader readily available right now so I can't check your app directly).