Lotsa stuff going on, so let me chime in a bit.
First, I agree with Liz, I think we need to do this conventionally...over the wall, from the sea, however. The magic stuff is easy, but expensive and we know they have far more magical assets than we do. Switching up entry and exit methods means they have a less easy time of preparing for us.
Second, the cannon idea is bad. Very bad. All that would do is lose us the cannon. Their aerial assets would simply swoop down and eliminate it. One cannon is also going to take a long time to take down that wall. For now, they serve us better to defend the town. They will also be good for any mass assault, should it come to that.
Third, someone mentioned the barracks (Gertie, I think). Considering how much trouble we're having coming up with a way to get the elves out, the barracks might be a better target. We get in, smash stuff, kill bad guys and get out.
Fourth, Liz mentioned lotsa info gathering still to be done. We can do some of that too, especially if we don't have a four hour hiatus this week

I think it's important that we take every opportunity to hit the bad guys when we can (ie every session).
Fifth, we are still hideously undermanned, but I believe Jaine mentioned that she will be on that, so something is being done to work on that.
Sixth, we have this special forces squad kicking around. We should probably utilize it, unless we're having them concentrate on training the next squad...?
I think that's it for now.