My main experience is usually with Napa. It's hard not to go to Napa and hit 6-8 wineries and not come back with at least a dozen bottles per person.
usually my process is go to the wineries, find what I like, and add on the bubble wrap sealed bags for the bottles. Then get the shipping box from the UPS store in downtown Napa (yes there is one, with really good hours) that is specifically designed to fit the bottles with extra padding. They will happily tape the box for you once done since you're buying the box from them.
Ship it as one of your bags on the flight home.
Customs has NEVER charged me ever for being over. They've asked the purpose of the trip, and usually napa has been some sort of celebration. They've asked how many bottles --- I tell them 12 (per person). They ask "how many different wineries"... I tell them honestly.... then they wave me through.
None of them want to go through every bottle to try figure out the small amount of duty on being over limit (since the duties are based on alcohol content)... and they appreciate us being honest.
Usual cost at the wineries for the bubble packs are $2-3 per bottle. $10-15 for the box at UPS in downtown Napa. Considering most of the bottles I buy in Napa are 35-40% of the price they are in Canada, I'm still ending up way more ahead....