My mother taught me to never throw away the liquid in canned vegetables. She says that is the basis of a good soup or sauce. The both of use that liquid as one would use stock. Is that good practice though? We don't like throwing anything away.
"How close" is really a matter of taste.
Canning liquid generally consists of water, salt, and preservatives, plus particles from the cooked vegetables in the can. For example, the can of chickpeas in front of me contains "Chickpeas, water, salt, disodium EDTA". Since a vegetable stock is usually made with water, salt, and an assortment of cut vegetables, this makes it at least somewhat similar.
However, it's different in detail. First, the liquid in cans is generally flavored only with one vegetable, and not usually the same vegetables you'd put in stock. It also tends to have more salt and preservatives than most people put in their homemade stock. Finally, the liquid usually has a much more concentrated and "cooked" flavor than you'd generally want in a vegetable stock -- it tastes like a stock that was cooked for way too long.
And, of course, it contains none of the amino acids and gelatin you'd find in a meat and bone stock.
So, could you make a base for a vegetable soup using the liquid from canned vegetables? Certainly, yes, and it might or might not be better than just using water. But it certainly won't be as good as a purpose-made stock.