If I entered 2017 marriage date instead of 2016. Do I need to change my 2016 return as well? What is the implication if spouse is not Canadian nor & no Canadian income?

It depends on when your actual change of marriage took place.  If your marital status didn't change until 2017, there is no need to change your 2016 return.

If your spouse is not Canadian and doesn't have any income, you would put the social insurance number as 000 000 000 and report the income as zero.