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.
Useful Links:
U.S. Department of Homeland Security
If your flight stops in the US en route to Canada, you may clear customs and immigration at that transit point. You will be issued a visa of sorts, but it is a transit/one day visa only. It will not apply to re-entry into the US.
If you do decide to enter the US from Canada and you haven't already organized a visa, it may be possible to obtain a short term visa at the border or at a local immigration office. There will be a fee. If it's a small border crossing you may need to have the correct change.
Not all borders have full time immigration officers, so if you require a visa to enter and there is no officer on duty, you will be turned away.
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.
Taking stuff across the border.
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 drugs. If you aren't sure about your prescription medication, get a letter from your MD.
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 out if requested by customs official.