Please note the information contained on this page is for general reference only. If you are considering crossing any national border by bicycle speak to a customs or immigration official prior to departure. Regulations will change so this is just a guideline.
NOTE: Have an account of your travelling plans available to show the inspector. If you have route maps that's good and be prepared to provide estimates of how long your trip will take.
For any expensive items (especially your bike, but also cameras, lap tops, etc.), complete an Identification of Articles For Temporary Exportation (for Canadians going into the US) or Certificate of Registration for Personal Effects Taken Abroad - Customs Form 4457 (Americans entering Canada). You can obtain these forms at the border or at your local customs office. Have the form(s) stamped at the border or prior to your trip. The serial number of the item is recorded on the form and proves the origin of the item. Otherwise the item could be dutiable (and in Canada, GST-able). Once completed and stamped, keep these forms, they'll be good for future trips. Non Canadian/US citizens should check with their own country officials for similar documentation.
The form(s) should travel with the item. If your camera is on your bike, keep the form with you. If your lap top is in a support vehicle, the form should be in the support vehicle.
In cases where the support vehicle will be carrying your personal effects you may want to write out a declaration for the driver. This should state which items are yours and that they are for your personal use only. A rendez-vous at the border with your support vehicle may be the best option. The person with the vehicle will be resonsible for the contents.
Know what you purchased in the country that you visited. When asked, itemize everything. There is no problem with purchases for your personal use, food, parts etc. Don't joke about what you might or might not have on your bike.
The amount of stuff carried on a bike shouldn't raise any alarms but if the authorities sense a hesitation you may be pulled aside for a thorough search. If this happens, co-operate completely.
Don't carry illegal drugs.
If you aren't sure about your prescription medication, get a letter from your MD. On that note it can be difficult for U.S. citizens or residents to get perscriptions filled in Canada. You are best to bring sufficient quantities for your stay.
Don't even think of carrying firearms or explosives across the borders.
Some food items will not be permitted across the border. Be prepared to dispose of them if requested by customs official.
It's in Canada and a great day to go for a bike ride!