(written from a Production point of view)
Michael Canavan (born 17 August 1953; age 64) is the actor who appeared in three episodes of Star Trek television series. His unfinished costume from the episode "Unforgettable" was sold off on the It's A Wrap! sale and auction on eBay.  For "Defiant", he filmed his scenes between Thursday 6 October 1994 and Friday 7 October 1994 and Monday 10 October 1994 and Tuesday 11 October 1994 on Paramount Stage 18. His makeup artist for this episode was Dean Jones.
Canavan is married to fellow Star Trek guest actress Shannon Cochran. In a StarTrek.com interview, Cochran mentions they married because he was the only other person, aside from Jonathan Frakes and Nana Visitor, she filmed the episode "Defiant" with. Canavan remembered working with her on this episode, too and mentioned that they both wore no alien makeup and he saw how pretty she was for the whole week. 
Canavan's other projects include the feature films Hidalgo and Murder By Numbers. His television credits include a recurring role on 7th Heaven as well as guest appearances on Alias, CSI: Miami, The West Wing, and The X-Files.