Get yourself a Y38 form from Canada Customs before you cross the border.
It's an easy way to save yourself a possible pile of grief and $$ when you come back.
I just found out about this. It seems it's been available for years.
I'll be getting one for whichever GT I take with me next time I head
south to an event.
Protecting your valuables
Before bringing highly valuable items with you when you travel outside Canada, you may wish to take advantage of a free identification service that is available at all CBSA offices. This service is available for items that have serial numbers or other unique markings. If the items do not have these markings, the CBSA can apply a sticker to them so that they can be identified for customs purposes as goods that are legally entering Canada.
When you show your valuables to a border services officer and state that you acquired them in Canada or lawfully imported them, the officer will list the valuables and their serial numbers on a wallet-sized card called a Form Y38, Identification of Articles for Temporary Exportation. This form is only available at the port of entry. If you are questioned about your goods when you return to Canada, show your card to the officer. This will help identify the valuables that were in your possession before leaving the country.