If I don't make a repayment to my Home Buyer's Plan is it automatically calculated and added to my taxable income? Or is there a form that I need to submit?

Are you required to make a repayment? There is a grace period of two years before you need to begin repaying. 

If you do not, you're correct. The non-payment is treated as income. 

If you are repaying, you need to complete Schedule 7 to designate the amount you're paying. 

If we get two years of a grace period then we should be fine until next year's tax season. Thanks for the info.