对朋友可以说：By the way, would you like to come to China?如果是长辈：I wonder if you will travel to China.
by the way, would you like to have a travel in China? 顺便问一下, 你要来中国玩玩吗.
By the way,what about coming to China for pleasures
By the way,would you to visit China in the futher?