1) If you are not leaving any goods in Canada (i.e. you are taking everything you bring in out again when you leave) then you are not subject to any import rules or requirements.
2) Besides proof of your own identity, the Border Service may ask you for information about the event, or some form of proof the race car is yours via things like title, registration, bill of sale, log book. What they want is assurance that you are not importing anything into Canada. It would be good to have a copy of the supplemental rules for the event handy. Or feel free to email chuck@enduroelite.ca to provide you with a letter confirming registration at one of our events.
3) Something to consider is whether or not your home country will want anything from you before they’ll let you bring your car home. Experience shows that returning to Canada after racing in the US the Canadian Custom Service is most interested in whatever “goods” are being brought back to Canada (so they can charge duties). You may need to be able to prove you owned the car and other equipment before you left your host country (log book, etc). Make sure you check your own border and customs rules so that you don’t run into difficulties on your way home.
4) DO NOT BRING WEAPONS OR DRUGS INCLUDING MARIJUANA INTO CANADA