About 5-6 trains everyday from between Shanghai and Guangzhou. It takes 16-24 hours (T trains are faster and K trains slower), costs 544/568RMB for soft sleeper. You can see Shanghai train schedule(https://www.travelchinaguide.com/china-trains/shanghai-schedule.htm) to know the time and other details. It will help you to choose a suitable one to take. Many flights between Shanghai and Guangzhou. Most flight from Shanghai Hongqiao Airport. It takes about 2.5 hours. As to the costs, 50 percent discount ticket is available if you book now. If you will go in early Feb or around that period, consider to book earlier. For it is the Chinese New Year. Only little discount or even full price at time time. Cheaper again in late Feb and March. Anyway, flight schedule, price, discount can be seen here in the Shanghai flights(https://www.travelchinaguide.com/china-flights/cheap-shanghai-flights.htm) . The weather in Guangzhou would be warm, still cold in Shanghai. I worn a thin sweater and coat in early Mar when I went last year.