Hmmm, yea, we can all get political and moral here very quickly, but I'd like to avoid that and cut to the chase if possible. I know, it's a situation that is so far out of my depth it's crazy, but for puppers, I'm willing to do the unthinkable, for good widdow boys, I can push myself.
Dogs seem to have a lot of the same pharmacokinetic considerations as us humans. For instance, the bioavailability is approximately 1/3 by the oral route when compared to the intravenous route. The most common indications for pain in dogs using Morphine is 0.5mg intravenously, so we'll extrapolate that 1.5mg orally is appropriate. From everything I've read, there isn't a correlation between breed/type and bioavailability or at least not a significant one.
You can assume that this is going to be 3-4 times per day to maintain analgesia, just like in a human, but you're going to have the added need to monitor how the first dose effects your dog.
Now, you're not even using Morphine, but poppy is a Morphine preparation. You should use a combination of things to determine an appropriate starting dose if you ask me. The first would be, how this preparation effects you. This will give you a broad, but useful benchmark from which to continue narrowing in on a good dose for your dog.
In the end, if you choose to do this, the biggest part of your responsibility will be monitoring the effects that it has on the dog and acting if you notice they're breathing really getting shallow. You can easily head to the vet or even do compressions yourself if you notice problems. You just need to pay close attention and really, the chances of things going very wrong are minimal.
I know it's probably not applicable here, but I would always recommend trying Cannabis before Opioids with pets, just like I would suggest for people.