That's pretty easy.

If you have a randomized controlled trial, the sugar dose is varied and other confounding variables are controlled by randomization. So you measure the causal impact of sugar only. There are studies showing that.

With observational studies, if you have a dose-dependent effect, then that's good evidence (although not completely conclusive) of a causal relationship. This is what many studies do.

If you have a meta analysis covering many primary studies, and if those vary a lot of context (i.e. countries, year, composition of the population), and you still get a consistent effect, then that's another piece of support for a causal relationship.

The few studies that I've looked at seem to show a pretty robust picture of sugar being a cause, but there might be selection bias - i.e. we'd need an umbrella / meta meta study (which ideally accounts for publication bias) to get the best estimate possible.

What are "the habits surrounding consumption of the beverage?" It's been my observation that soda drinkers drink soda all day, no matter what they are doing.