I'm not a male gamer, but I don't see why it matters since I play both male and female characters. Plus, I'm a lesbian, so as far as my personal preferences go, obviously they'd be between Isabela and Merrill. I think Merrill is adorable and shun everyone who could possibly hate her, but she's more of a little sister than a romantic option for me. Isabela, though, is beautiful, independent, strong, and sensual. She's a dream.
Also, lol... I thought the Bioware forums were over the "OMG Anders hit on me and it made me sooo uncomfortable" whining but apparently not. Get over it. Sometimes people will like you and they will make the first move, even if you don't reciprocate romantic interest. Anders does the same thing for a female Hawke, too. Turn them down and move on.
I always assumed that Anders and Isabela were the more "canon" love interests. Isabela of course kisses Hawke in the trailer, but Anders seems also like he's one that Hawke is supposed to get with. Just like in DAO, Alistair or Morrigan seem like who the Warden is really "supposed" to get with.
But I only play gay romances, and whenever I play male!Hawke with the intent of romancing Anders, I just get too caught up in Fenris's puppy eyes... damn him!