i m thinking of visiting Guangzhou sometime from Dec 26 for a couple of days? Will it be too cold?

Hi, it will not be cold then, just cool actually. At that time, the sverage temperature could be about 16 C or a little higher. From time to time, the lowest temperature can be only 10 C. In any cases, it can be a good traveling time.
By the way, you can wear long-sleeved shirt and prepare a light coat to keep warm at cool nights.