My 2 cents is that the US/China issue will not be solved at the G20. Sure there might be a communique of some sort announced that will dampen volatility temporarily, but this US/China friction is more fundamental than to be solved at the G20. I think it is not as much about trade as it is about countering China policies regarding intellectual property and technology transfer from US companies to China. That is the main focus of the US trade representative Robert Lighthizer and he said that is not going to be easy.
All this is not to discourage you, but the saga of US/China will continue. Seeing as Trump likes to play unpredictable, maybe a good entry spot for your trade would be to capitalise on an uptick in vol pre the G20.