In a nutshell
Your visual identity is how you translate your purpose into visible elements. It can be defined as the collection of all brand elements that you create to portray the right image of your brand. While the Values will help your employees taking the right decisions and having the right behaviours, the Visual Identity will ensure your customers/clients to recognise (without any doubt) who you are and why you exist.
In the Marketing Canvas
In the Marketing Canvas, we have identified 6 main categories for building your Marketing Strategy: CUSTOMERS, BRAND, VALUE PROPOSITION, JOURNEY, CONVERSATION and METRICS. Each of these categories, have 4 dimensions which means that a total of 24 dimensions (6 by 4) are defining your Marketing Strategy.
VISUAL IDENTITY is a one of the 4 dimensions of the BRAND category.
How to use it?
David Aaker, hailed as the Father of Modern Branding, defines brand identity as, “…a unique set of brand associations that the brand strategist aspires to create or maintain.”
Jeff Bezos puts it in slightly more colloquial terms: “Branding is what people say about you when you’re not in the room.”
Mark Bower, says: “Your brand identity is how you project yourself to – and how you want to be seen by – the outside world.”
Source: Woven Agency Blog 
Brand is your logo and visuals, too. A great brand deserves a great logo and great graphic design and visuals. It can make the difference when the customer is choosing between two great brands. But these alone cannot make your brand great. 
In the Marketing Canvas, we have started with the Purpose, Positioning and Values. These dimensions are key tenet of your Brand. And as mentioned in the Harvard article, a great brand should have these elements right. We usually start with the logo! Most of the startups spend time (and money) on finding the right logo when sometimes the reason why they are existing is unclear. Don’t take me wrong! A great and robust visual identity is key and you should take this very seriously.
VISUAL IDENTITY is defined as Way you would like your practice to be viewed .
If we refer to Kapferer’s PRISM (a model that helps building a brand) , the VISUAL IDENTITY is composed by the PHYSIQUE, RELATIONSHIP and SELF-REFLECTION elements.
If you are interested in this topic, please have a look at InkBotDesign article on Brand Identity. You can also read the book of Kapferer if you want to go deeper in the subject.
For the Marketing Canvas,
Your Visual Identity is a Brake if you are unclear about how people should remember you. You are not differentiating yourselves with your Competitors (Context). You are not amplifying your Brand Purpose which will have a negative impact on your performance. It will play against your ambition.
You might have a very clear VISUAL IDENTITY (accelerator) with an unclear Purpose (Brake). This is an interesting scenario because it means that your logo (and all the other elements) are very clear and differentiate yourself but has not meaning (or unclear). These are typical cases of Brands are sexy but empty of sense.
Best situation is when your PURPOSE is strongly defined (Accelerator) and your VISUAL IDENTITY is perfectly portraying it (Accelerator). Like NIKE.
Is the VISUAL IDENTITY of your Brand helping you achieve your goals?
Woven Agency, https://woven.agency/blog/what-is-the-brand-identity-prism/
Harvard Business Review, A logo is not a Brand, https://hbr.org/2011/06/a-logo-is-not-a-brand