Sounds like an interesting trip.
You'll need local insurance in Canada and the US. Check out progressive.com for one option to solve this.
As for shipping, sounds like the chap you were talking to was referring to shipping by sea. Look at the shipping section here on this site to get an idea what people have been paying by sea or by air to different destinations. You may find that a lot of the costs (eg. port fees) are somewhat high so that shipping by air is a viable option. Your bikes are light so I would guess it would be pretty reasonable.
Sounds like you are committed to your selection of scooters to do the ride. I'm sure you'll have fun.
Nothing against scooters, but as someone who enjoys the riding as well as the travelling part of those trips, I would choose a much bigger bike. The distances are vast, and I'd like to be able to outrun the wildlife up north if the necessity arose
Down south, the speed bumps can be exceedingly large so clearance can be an issue on small bikes.
Having said that, if you are used to touring by pedal bike I'm sure a scooter will seem like luxury.