Put your possible deal breakers up front and mention them soon before you get too much invested. There are people out there for whom poly is a plus, not a detriment, but if they can't see that you are poly then they can't pick you for it.
I have a profile up on OKCupid, and it says in the second sentence that I am poly. I also include a link to a good information site for those that are curious. If the guy is NOT polyamorous or open to it, then I don't want to get attached in the first place. People who are interested are out there, but, it needs to be visible so that they can find you.
The deal breakers being upfront and visible thing is good for other things as well. If you adore your (pets, trombone, favorite food, lover) and won't want to deal with someone who can't handle being around your (pets, trombone, favorite food, lover) then mention it on your profile! People who have similar interests can then find you and you won't spend time getting attached to someone who can't handle that you have a Great Dane, or play the bagpipes, or are married.