Right now, China could not win for the same reason Napoleon couldn’t beat Britain in 1805: IF the Chinese today, or the French then, could get across the water, they would manhandle the little island on the other side, which they vastly outnumber(ed).
But Napoleon didn’t have a navy to do it, and China doesn’t have one...yet. However, time is on the side of China. They have almost a trillion dollars in trade surplus pouring in every year. Their industrial base is skyrocketing. With each passing year, they can build a bigger and bigger force. Taiwan cannot possibly keep up, and the technological edge over China is eroding.
With time, the defense of Taiwan would require either the intervention of the US, or Taiwanese nuclear weapons. I myself prefer the proliferation route. Taiwan and Japan both need nuclear weapons of their own, to safeguard them against attack by China.