Attributes dimensions for shipping

Hi!
I'm trying to setup some attributes and options, but I have encountered a problem.
I've got the Canada Posts Module, and that modules asks me for the sizes ans weight of the product... but only for the main products.

Example: I can ship the same pet food in size 5lb, 10lb and 25lb. Obviously different weight, but also different dimensions...

Is there a way to put those dimensions in the attribute description, so that my shipping module can use them?

Thanks a lot!

Attributes can have weight adjustments applied, but out-of-the-box size/dimension adjustments are not so applied. I think I have seen some creative ways to address one or the other aspects from applying a specific weight across the cart to activate one method of shipping or another or a particular cost aspect to it and use the weight factor as is where the shipping "cost" would apply/activate/relate to the shipping. Dealing with dimensional data becomes difficult when working with multiple products in an order, but is at least in part handled by the plugin OzPost used in Australia. But that's a little of a different story.