Interesting puzzle idea! We've actually tried something like this before. What we found worked best was having slightly more complicated mazes, instead of large open areas, and to make it so that you needed to get the different objects you're controlling to different locations.
In your game as it currently is, all you need to do is focus on getting all the dots to a single corner of the level, and then from there it's pretty easy. Trying to keep multiple dots in multiple locations could provide more interesting puzzle designs, and a bit more variety. Once I'd completed a few levels of Can We I felt like I'd kind of seen everything the game had to offer. That variety is crucial I think.
Hope the feedback is useful, and hope you had fun making this game ^_^
(-Joe)