you have no idea what a trouble i had ----you this present A

如果选择to find,是为了找到这个礼物
选择C.finding,意思是找到这个礼物,强调结果
不过,你的句子中有错误,不能说what a trouble,要说what trouble
You have no idea what trouble I had (finding) you this present.
你不知道我给你找到这个礼物费了多大的力气.