I would argue that they are not the same, but you are correct that there could be some overlap. I think you will also find that people in different schools of thought might prefer a particular term for philosophical reasons in some situations, and in others the terms are more clearly distinct.
I would say that volition involves conscious decisions to do certain behaviors: that's it. In my experience, "volition" isn't often used in neuroscience and psychology, it comes up more often in philosophy. It may also be used in psychiatry but that is a field I am less familiar with. Similarly, self-control and willpower are not typically used in studies of the biological basis of behavior, except to relate to more colloquial discussions.
Cognitive control (see Miller, 2000 and Ridderinkhof et al., 2004) is similar but often involves inhibition of some unwanted behavior. It often comes up in the context of addiction as something that is absent/lacking, or in suppressing attention to an otherwise distracting stimulus. Cognitive control is also used to refer to error detection and behavioral correction, keeping focus towards some future goal. The neural correlates of cognitive control are usually identified in the prefrontal cortex.
Motivational salience (see Berridge & Robinson, 1998, Ventura et al., 2007, and Bromberg-Martin et al., 2010) is in many ways the opposite of cognitive control. Often, cognitive control is marshaled against other salient motivations. For example, in addiction, you could say that there is a high motivational salience towards the rewarding features of a drug: in someone with an addiction, those salient rewards motivate future use of the drug. Suppressing motivational salience in order to achieve some other goal (for example, sobriety) requires cognitive control. The neural correlates of motivational salience are usually identified in the ventral striatum or amygdala.
Berridge, K. C., & Robinson, T. E. (1998). What is the role of dopamine in reward: hedonic impact, reward learning, or incentive salience?. Brain research reviews, 28(3), 309-369.
Bromberg-Martin, E. S., Matsumoto, M., & Hikosaka, O. (2010). Dopamine in motivational control: rewarding, aversive, and alerting. Neuron, 68(5), 815-834.
Miller, E. K. (2000). The prefontral cortex and cognitive control. Nature reviews neuroscience, 1(1), 59.
Ridderinkhof, K. R., Ullsperger, M., Crone, E. A., & Nieuwenhuis, S. (2004). The role of the medial frontal cortex in cognitive control. science, 306(5695), 443-447.
Ventura, R., Morrone, C., & Puglisi-Allegra, S. (2007). Prefrontal/accumbal catecholamine system determines motivational salience attribution to both reward-and aversion-related stimuli. Proceedings of the National Academy of Sciences, 104(12), 5181-5186.