We bagged our birds in clear plastic bags, first Ziplocks the first decade or so then vacuum packed the next decade with the feathered wing visible through the bag. It took a little jockeying around but we could get the speculum of the ducks visible for inspection before freezing them. The Border Patrol agents would check the first handful then glance at the remainder. It was pretty simple for them as all we would bring back were mallards, pintails, snow, speckle belly, and Canada geese and maybe some cranes. We would even go somewhat out of the way to drive through the entry at Hansboro, ND as we had a good relationship with the agents there.
Something to keep in mind is the larger entry points are often training sites too so you may be checked more thoroughly there than smaller entries. Often, one will see the same agent(s) on the way back which can make an easier transit if you made a good impression with them leaving the States. We would get the declaration forms on the way in to Canada and, if they weren't busy, ask for pointers on how to best fill out the forms. We would also ask if the agent would look over the firearm ownership form to see if any mistakes were made. Being polite and asking if they had the time to do this went a long way towards making re-entry to the States quick and painless. It's been 5 years since I hunted Canada but friends have been there since plus I traveled back and forth a few times a year for other reasons prior to the Wuhan flu and these are my observations. Good luck on the hunting.
