Equivalent here is a noun, the basic meaning of it is “相等的东西，等价物，对应的东西”. When you put it in a sentence and try to translate the sentence, I think you rarely find the same words in the translation. Take the sentence you gave out as an example：对于女士，我们送鲜花，那么对于男士我们送什么呢？ equivalent adj. 相等的，相当的，相同的，对应的

“相当于”是最标准的说法，还可以说“如同”

Indeed, you can translate your original sentence with the expression you suggested. 給女人一束花（的意義），相當於（或、等於）給男人什麼呢？

I don't think the meaning of "What's the equivalent of giving a woman flowers for a man?" is "what should we give men that will have the same meaning as giving flowers to women" ,"equivalent" its Chinese meaning is ”等价物，相等物，等价的，相等的，同意义的“，I think the meaning is that "except giving women flowers,what else can men give to take place giving flowers but has the same meaning as giving flowers just for showing our love to women .除了送女人花，男人可以送什么来代替送花但是跟花有相同的意义来表达我们对女人的爱呢"I don't know what the exact meaning the writer want to express.This is just my opinion.Hope you can point out my mistakes.Thanks.

贈美人以香花猶如贈男仕以何物 贈美人以香花猶如贈壯士以寶劍