And then there is this option....Maybe not the smartest, but an option.
Knew someone who did not know about Canada's strict laws, but encountered a very nice border agent in the early eighties who politely told him no handguns. The crossing was in a remote section of Montana, basically the middle of nowhere. The agent mentioned a solution he had heard of, and the fella trying to cross took it to heart. He traveled about a half hour back down the road, found a spot he could easily find again, went deep into the woods, and buried his two handguns (broken down and bagged in ziploc bags) in several spots where he could find them again. He said the only problem for him was having to go out of his way returning to the US to get them (he planned to return via a different crossing).
But since you know ahead of time, just leave them with a dealer or someone who can care for them