Probably going after nectar...

You want to look for aphids up in the flower and the leaves and the meaty parts. Ants going up and down the stems might be them collecting nectar from the aphids the ants "farm" (although more like herding wee nectar cattle). They protect the aphids from predators and the like and the aphids multiply like mad.

It can be quite bad on some plants, don't know about sunflowers. The aphids can really harm the plants but it's the ants that are 'causing' it, sort of. Having that this year with a young cherry tree.

I am familiar with this! bane of our gardening exsistence haha i looked and didnt find any but i will neem any way for good messure!

I guess it's possible they're just climbing up for the view and the sunlight.