If you want to eat vegan in China you have to learn basic Chinese. There's no way around that. Given that, it's fairly easy to get proper vegan food for very cheap. There are tons of small restaurants, everything is cooked on the spot.
There are also many completely vegetarian restaurants, 素食餐厅 sùshí cāntīng (this sounds more like rather like suusheh tsahnteeng than like "sushi cantine").