Really cool idea :D.
Really good work on this. There's a few flaws, for one the randomizer for the level design sometimes places bombs right in front of entrances >.<. It's nice the super bomb destroys them but it would be nicer if there was a inexpensive way to get rid of them ,perhaps give them a ton of hit points and vulnerable to lasers, or add a tool to the shop that can remove traps after several hits from it.
Also there's an odd glitch I encountered when adding a second cannon, where I had drawn my little cannon in the middle of the box, but after hitting space for the placement it was about a inch to the left from the right spot 0.o.
Lastly it is a bit too easy, though I enjoy a casual game myself, but perhaps you can add easy and medium difficulties in the next one, wherein the medium difficulty has a "pencil lead" meter, akin to a energy meter in some other shooting games, limiting how much you can shoot. It would recharge by itself but force the player to be careful with their shots. That's all my own suggestions, but whatever you choose to do, I look forward to the next version! ^^.