I started on a massive ramble about CA vs. CPA but I really don't want to get into it. It's far to difficult and confusing to explain in writing, especially considering how much of it is personal opinion.
Just to note, if you still want to study CA but haven't met the requirements, they've recently started offering a "foundations program" which would allow you to complete the areas of knowledge you're missing before starting the CA program. Think of it as taking a few extra classes and it should pass by quickly enough!
Anyway if your double degree is anything like mine, you'll probably have a tonne of electives you'll have completely forgotten about. Enrol in the subjects you need and you'll have met all the knowledge areas!