You definitely want all your paper work in order.
Are you talking about crossing the tunnel or bridge.
Or going across in your boat? They used to have a
number to call but they might have changed that after
9/11. You might try looking up the OPP on the net.
You should always have the boat and trailer registration with you. I have only been asked once for it, but had to get out of the truck and pull it out of the boat. Now I have it up front with me to make it quicker.
I trailer over often in the summer and have never called anything in. Just drive through and say I am going to xx to go fishing.
Make sure you have your proof of citizenship handy as well.
When you drive your trailer across the bridge or tunnel, they might ask you for an I-68. They might not. They made me pull over a couple years ago and fill out a temporary import form for my boat asserting I wasn't selling it or transferring it to a Canadian citizen, and that I had a limited amount of time I could have the boat in Canada. It was no big deal.
One thing we covered at the last federation meeting is that they are now enforcing the regulation on having your positive battery posts covered in your boat. If they check, you must have this. They don't give warnings in Ontario, just fines. It's apparently law in Michigan too according to Spitler. It is a good safety idea.
DON'T have a flare gun in your boat. This is a SERIOUS firearm violation in Canada. You will not pass go and you will not collect $200. Ontario will collect a bunch of your hide though and you will be a felon and no longer wanted in their country without paying another large fee before they let you in again.
Have an original copy of your birth certificate on you along with all your registration papers.