A, only the population of Shangcheng District is less than 411,111, so the option is wrong;
The population of B, Xiaoshan District and Yuhang District exceeds 1 million, so the choice is wrong;
C, the sum of the population of Shangcheng District and Xiacheng District is lower than that of Jianggan District, so the option is wrong;
D, the population of Hangzhou has exceeded 6 million, so the choice is correct;
therefore, choose: D.