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.

Enam, I would not worriota out it. This is a natural link. Think of other social networks like twitter. If you were to tweet your link and 10,000 users retweet it, you have that many links from different pages within twitter.com

this s the nature and structure of the website, don't stress yourself about this. If this was coming from a crappy domain or spammy bloon other it would be something to worry about.

I hope this helps. Have a good weekend.

I agree. Just another link. Even nofollow links are good links, but no, this one is not a nofollow link. It's a dofollow as they say..link :).

Andrew, let's site abc.com is the site linking to your from their homepage. If you really want to check, just see cache:abc.com in Google and see if the page in Google's cache contains your link. Google may or may not show all of your backlinks.

Considering your site is new, and the fact that you are doing Guest Posts (which in my opinion are the Directory Submissions of 2011-2012-2013 years), I would look at diversifying your link building tactics to be more natural. Really natural. Specially if you want this site to rank for a long period.

I hope this helps.