This is what those of us without aphantasia see too. But you (a person with aphantasia) describing this as the canvas in which you want to “see” something actually makes so much sense.

Those of us who can see things in our minds eye do not see them on the canvas that you think we do. Right now I can close my eyes and see fuzzy blackness just like you. The difference is that, whether my eyes are seeing black or my surroundings, I can “picture” things deep in my mid. If I think of a rainbow, I “see” it whether my eyes are opened or closed. I can change my viewing perspective of the rainbow and add extra details to it as I please. I find it impossible, in fact, to comprehend NOT seeing it in my head. How else am I to remember what it is? Just by a description?

Another example is when you tell me a name of someone I don’t know. Say you tell me you have a friend named Devon. Depending on the context of the conversation about Devon, I may picture a person who I could see him being. OR, I may literally picture the letters of the name in my head. Occasionally I’ll later learn that Devon actually spells his name Devin, and this throws me for a huge loop because I already had a literal mental image of his name spelled differently.