Some domain management companies let you do a 301 redirect of a domain to another domain...however they might only do domain.com to newdomain.com not specific/individual and customized redirects.

Is this a wordpress based site ? What CMS are you using ? How were you able to get domain.com/sample and domain.com/sample.html be the same page ? Either way, canonical tag is the correct solution in this case. There's no need for a 301 and if you do 301 redirects, you are not really fixing the issue caused by your CMS System.

I would therefore strongly advise to use the canonical tag. That's the intended use of that tag.

If it's great content, it might make more sense to keep it on your website. Some blog posting is okay, but too much of any one kind of links will only cause issues, both short term and long term. Think about Directory Links 5 years ago. Everybody got 500 Directory Submissions for $50 and so on, and those are the kinds of links people are getting Unnatural link warnings for.

So I'd recommend evaluating your link strategy and only build quality links, rather then faster links, instant approval links, focus on quality and user engagement vs quantity.

I hope this helps.