I reached out to Weebly and their response was "Yes you can add canonical reference in the header window under the setting tab in the SEO section"  So it looks like this would be applied and the site level versus the page or post level.  I did open the blog posting area and there is only a spot for a category, permalink, seo post title and seo post description. Looks like there isn't  much I can do at this point.

Anyone familiar with Weebly that can offer some suggestions?

I ran a crawl diagnostics on my site and have some high priority issues that appear to stem from Weebly Blog posts.  There are several of them and it appears that the post is being counted as "page content" on the main blog feed and then again when it is tagged to a category.  I hope this makes sense, I am new to SEO and this is really confusing.

Thanks!