Welcome to planDisney, Daniela.
Congratulations on your upcoming Disney Wedding! Alaska is my family's favorite Disney Cruise Line destination. I can't imagine your fairytale wedding will be anything short of positively magical in that awe-inspiring setting.
My family and I recently returned from an amazing cruise aboard the Disney Wonder. As we approached our final port of Vancouver, British Columbia, I noticed that we could check the Disney Cruise Line Navigator app for debarkation information, including Canadian customs allowances and instructions for filling out Canadian customs declaration forms. But I think it's even better that you are researching things in advance to understand what to expect.
When we arrived in Vancouver, we had to fill out a customs declaration form, such as an E311 Declaration Card from the Canada Border Services Agency. When we transferred from the cruise ship terminal to the Vancouver International Airport, we had another form to fill out for travel to the US, such as the US Customs and Border Protection form 6059B. In both cases, the process and required information were similar. Both countries also have similar restrictions related to plant material. I understand this would preclude the import of fresh flowers from your cruise. I'm sorry that's likely not the answer you were hoping for, Daniela. If you'll indulge me, perhaps a few other comments might inspire an option that is "practically perfect in every way" for you.
First, I recommend contacting your Disney Wedding Manager or Planner ahead of time, as well as speaking with your Onboard Wedding Coordinator after you board your Disney cruise ship to discuss the best options for preserving memories of your bouquet and floral arrangements. Faux flower options, such as silk flowers, may be a possibility to retain those mementos forever. If your fresh flowers have ribbons, charms, or other decorations on them, those pieces could also be keepsakes for remembering the lovely floral arrangements from your wedding. I've also heard of brides enlisting an artist to recreate wedding bouquets based on detailed photographs, but using high-end silk. Such an artifact would look lovely in a shadow box to display along with cherished wedding photos. As for the fate of fresh flowers onboard, some brides choose to give them to their stateroom hosts, dining service teams, or other crew members who helped make their wedding cruise especially memorable. The thought of wedding flowers taking on a second life of bringing happy memories to others might help make the thought of possibly separating from them easier.
I'm wishing you a most magical Disney wedding cruise, Daniela! As fellow Guests like you, it would be our pleasure to answer any more questions you may have as you continue to plan your fairytale wedding.
May all your dreams come true, Daniela,
~Tony