Advance notification is only required when you are exporting a vehicle (car, truck, rv) from the U.S., and then you only have to give the notice to U.S. Customs, not Canadian.
The 3 working days is to give them time to check the vehicle identification number (VIN) againt the stolen vehicle registries to make sure your hot deal is not "hot".
If you're doing a vehicle, watch your timing - when I brought my truck up the only guy who could approve the export only worked Monday-Friday, 8-4:30. Miss him and it's come back the next day.
At least that was the case 4 years ago, may have changed - always phone them ahead of time and get the current procedure.
The Sea Ray should be a good strong boat, Congrats, and before and after pic's are always nice to see.