Auto post duplicate content

hello
I have a script can auto repost my site's content to weebly,blogger,medium
But as I know, duplicate content is bad for seo.
and rel=canonical is needed to change each blog page,
it's difficult for me to change it.
So what should I do auto repost content to weebly,blogger,medium to
avoid duplicate content?
Use spin content is ok to repost duplicate content?
Thanks any advice.