Can I freeze stock and can later?
If it was frozen immediately or quickly after coming off the heat, then it's not much different from "fresh" stock. Food keeps indefinitely in the freezer, safety-wise, and the quality isn't going to be impacted very much because it's mostly water to begin with.

Just don't can any meat products that have been exposed to room temperatures for more than 2 hours, and follow the same safe canning practices (i.e. pressure-canning) that you would for any low-acid product.