The numbers aren't too bad right now; this could go either way. The break-down is what we've seen in all these campaigns before: women, younger people, Democrats, and urban areas are more likely to be OK with same-sex marriage.
The LGBT side of the question is already doing a better job with the ads and framing of the debate. Now they want more volunteers to show up and do more than phone bank:
And here's more polling idea, getting at the same general idea, but with a different framing:
It's close now, but the Maine No campaign has better ads than the Yes campaign and seems to have learned many of the right lessons from the No on 8 Campaign in California (ads that appeal to the state's populations and character, keeping same-sex couples prominent in advertisements, responding quickly to rightwing lies, getting volunteers involved with more than just phone-banking). If they pull this one off, this will be the campaign for the rest of the country to study.
(If this issue is important to you, consider donating to the campaign to help them keep ads on the air and their staff working.)