Interesting premise, but I think there are two assumptions that are pretty off-base. First, you’re wildly overestimating the ability of the PLA to take and hold hostile territory as opposed to acting in a glorified police role. Second, even Trump could be persuaded to provide a huge amount of food aid to India to keep its people from fleeing across the border. That would also plug in nicely to his “prop up farm incomes during the trade war” initiative.
The US does not actually "feed the world", it _helps_ feed the world. The amount of food the US produces only enough to feed around another 100-150 million people besides the US population, if they ate only US product. Maybe twice as many if they lived on a near starvation diet. There are over 1.3 billion Indians, which Canadian agriculture could only feed a fraction. There is no way the US could increase food production enough to cover the difference, even if there were time to do so. I'll agree China is rather wanked here.
It’s also worth noting that China is de jure a hair larger than the US and that the US would end up ISOT’ed there, while Indonesia and India would be in the US and Canada respectively.
The numbers do vary quite a bit depending on whether one is counting water or not and whether that water includes coastal and territorial waters. Room for quite a bit of playing around with the locations of India, the US and Indonesia.