Passports are now required (or the passport drivers license if your state has them).
Sleds and trailer must be licensed and have the registrations with you at the border (if they ask for it).
Join the Revelstoke Snowmobile Club if you will be riding multiple days...this will save you $ on the daily trail pass fee...and support a great club.
I dont know anyone from the states who has ever registered in Canada (not even sure if you can if not a resident).
As for insurance...call your insurance agent...they will have the answers (we've never had to make any changes...but we carry full coverage on the truck and trailer).
At the border...dont be a smart a$$ or a comedian. Answer the questions honestly and you wont have a problem. If you lip off to the agent, they can make your crossing a nightmare.
Have your passports and registrations ready...make their job easier and act like this isn't your first rodeo.
Also, if your cellphone carrier has a "North America" option, change over on the day you leave, and change back when you return (verizon allows this twice in each billing period).