Although I don’t tend to make oil cakes (because I don’t like the gummy/spongy texture of them), I have used canola oil, but I prefer to use a nut oil to give more flavor ... although I know the purpose of canola oil is its neutral flavor.
As I understand it, you can, generally, melt butter, although you might require a little experimentation, as butter is about 80% fat/20% water, and oil is, of course, 100% fat. That said, in Rose’s “redo” of the Cordon Rose Banana Cake (which I, personally, consider perfection in its original form), she subs 2T of oil for 2T of butter directly.
What is your specific problem with canola oil? That it’s often gmo? That it’s high-temp processed and so very bad for you? That it’s a polyunsaturated fat that can’t withstand heat without going transfatty or rancid in your system and, thus, wreaking havoc to your body? Maybe we can help find a sub based upon your particular concern.
Some use coconut oil, which—especially if you choose a raw, unrefined one—should be relatively benign, as saturated fats withstand heat well, and if it isn’t processed and messed with, it shouldn’t be trans-fatty. Most other nut oils will have the same high temp problem (whether through processing or simply through heating in the cake), as they are all mostly polyunsaturated fats.
Of course, cake’s aren’t health food by any means, so, likely, the best solution is moderation—however, there’s nothing wrong in trying to mitigate the bad stuff where you can, right?