keep both cards...
furthermore no gst next year and amex no annual fee...why want to cancel amex...

if your primary reason to get a 2nd card for shopping, perhaps Citibank Rewards/Cashback cards would be better?
Since your Wise already maximized, it's hard to "downgrade" the benefits to other cards  This is the only card that gives >5% cashback, and since your spending behavior already adjusted to meet Wise's benefits, it's better to keep it. Unless, of course you planned to STOP using Wise (about 2 months earlier) and cancel it due to high AF for Wise Platinum.

Keep your current Wise for your usual petrol + mobile + dining spending. Please cancel the AMEX Gold. 
M2C Amex is the better card to complement Wise. Limitation to M2C Amex is the 5% cashback only limited to weekends transactions. Moving Wise to Amex means you need to swipe all your usual transactions exclusively on weekends.

'sides, M2C has signup promo with RM100 rebate (note: 2x RM50 GST is currently imposed to new application). This is literally ZERO commitment for year 1 considering M2C has no AF. Furthermore, most likely, current credit card GST could be abolished by 1 Apr 2015. Let's hope Maybank doesnt introduce AF for M2C (which will be taxable at the rate of 6% GST next year).