LOL the odds of them actually checking your meds are slim to none. I think valid ID matching the stickers on the bottles would be fine even if they do.
As marcerella02 said, if you don't TELL them the puppy was bought on your trip, I doubt they'll ask. In the interest of covering your behind though, having the breeder write you a receipt for a small amount would be best, so you don't get dinged too heavily.
When I brought my sharpei Tequila across the border from Ohio 6 years ago, I was in the car with a sharpei breeder who'd also gotten a puppy. So there we were, a senior and a mid 20's woman with 2 7 week old sharpei puppies. We declared them (we both had receipts that said $100 but we'd been gone less than 24 hours, so we weren't allowed to bring anything back without paying duties) and we were told to pull over, go inside and pay the duties. In the time it took after parking to undo our seatbelts, the car was surrounded by 5 big, male, border guards. I about had a heart attack. We crossed over about 3 a.m. and I guess they were bored - they all came out to see the puppies. LOL After playing with them for 5 minutes, they let us go without paying a dime
Honestly, if you have nothing to hide, you really don't have anything to worry about. You've probably spent more time asking questions about what to expect then you'll spend with the border guards. Most of the time, at least going into the U.S. we barely get asked any questions, they want to skip to petting the dogs

Even coming back into Canada, many of them just ask questions about what kind of dogs, aw they're so cute, etc.
Tara