Do i need new simcard for data over there?
What is the best way to access whatsapp,use vpn?
Which is more easier to use and have wide acceptance,alipay,tencent?

Without China Simcard / (China) simcard data package from shopee, you can't used certain app such as DIDI or scan menu on table and order food.

You can used Data Roaming service which you no need vpn. Or used VPN if you used sim card which I mention above.

Our Touch N Go are China Alipay identical twin. You can used our T&Go E wallet app anywhere in China (Scan or Be-scan) but some shop only accept tencent pay then just pay with cash.