Bro, you are just wasting your time by continue to this discussion.
Most of blogger complaints, they have enable https in blogspot domain, but it is not redirected, so both http and https version are available, so to prevent that type of duplicate issue, we need to add canonical link tag with https URL. But if you already know about template code, then you have surely have idea about this code.
<b:include data='blog' name='all-head-content'/>
This single line add RSS Feed, Canonical Link tag, Post meta description etc. So there are no any customization facility to add our custom https canonical link tag.
While if you see Google official some blogs, then you will see, they are using https with canonical link tag, but normal blogger can't use it, I don't know why.
So It is good idea to don't use Https in blogger blog, If your blog is not redirect automatically from http to https or you can't use https canonical link tag. That's it.