They are safe to use for canning as long as they are thoroughly defrosted and brought to room temp before being used in an approved canning recipe. However, it is unlikely that you will get a whole canned berry worth eating, especially after having been through the freezing process. It's not recommended because the end product is likely to be excessively soft and mushy, basically berry pulp. If you would like a canned product worth eating from frozen berries, I would suggest you turn your berries into a jam, jelly, or syrup between the freezer and the canning pot.

Thank you, this helps a lot