I wouldn't recommend anything that sticks your iPad to your window. Firstly because its a large device to be covering your viewing window and secondly the weight of the device will be an issue for something like a sucker holding it to your window.
Try a mount that you can use in the vents like the Breffo Spiderpodium Tablet. I use it in my car:
Looks cool, unfortunately no options to put it in the vents here. I'm wondering if there isn't something around that I can stick on my dashboard and the iPad mini.