I think it's safe to say that the lore would support a pretty good range of male viera appearances. Since we've never seen them, and the lore is rather vague, they could really vary between feminine and masculine. Obviously, ignoring the fact that we shouldn't see them, like Miq'ote males, there's some real variance that might happen.

According to Viera lore, the males are indistinguishable from females until around 13, this means they COULD end up looking very feminine into older ages as well, if still not quite as feminine as females. On the other hand, most are considered, and consider themselves, outcasts from their matriarchal villages. This leads most, if not all of them, to lead a rather feral and secluded lifestyle in defense of the forests they call home. This COULD result in many of them looking quite masculine and rugged.

I'm not going to be surprised if SE goes with either of these options really, and I would be pleasantly surprised if they implemented both somehow, as I really enjoy both ideas personally. If I had to pick one I'd probably be most happy with a more feminine and lithe male design though, as it's not really something we've seen explored as much.