You could call yourself Esquire as long as you are very careful not to ever give legal advice or anything like it. Since lawyers more or less “own” this title – although I don’t believe it is actually tied to legal licensure – lawyers who are jealous of your use of the title will be quick to mount a complaint of “practicing law without a license” if any kind of case can be made.
By the same token, you can call yourself “Captain”, as long as you don’t pretend to rank in military or civilian service (such as police or firefighting forces).
You can call yourself “Reverend”, and no one can stop you as long as you don’t pretend to any particular denomination or ordination that you don’t actually have.
Since hereditary titles have no meaning in the United States (and Canada, too, I believe, but I’m not so certain of that), I’m sure you could call yourself “Sir”, “Baron”, “Count”, “Prince”, “Sheik”, “Emperor” and other terms like that, again, as long as no query elicits a response from you that pretends a rank in a place where you don’t have it. For example, you can’t pass yourself off as the King of England, as that would be fraud.