My wife and I are planning to visit Spain. Currently I am living in Canada and she lives in Iran. From what I understand, we have to submit two different applications. Since we are submitting two applications, I want to know how can I submit documents to show that I will financially support my wife? What are the required documents? Is it possible at all? Or should she submit her own proof of financial support?
It is possible, and very common.
You can provide the same documents that you will provide for yourself, for example a copy of your bank statements and savings accounts. The online form will give you an option to select if you are financing yourself, or if others are financing your trip. Your wife should select the 'financing by others' option. You can also include a cover letter detailing this if you want.