By car
Canada has a land border with only one country - the United States. See the "from the United States" subsection for more information on what to do when leaving the US.
You might also enter the country by road from the United States through one of many border crossing points. Obviously, the same rules will apply here, but if your case is not straightforward, expect to be delayed, as the officials here (especially in more rural areas) see fewer non-U.S. travelers than at the airports. Also expect delays during holiday periods, as border crossings can become clogged with traffic.
Drivers of American cars will need a Canadian Non-Resident Insurance Certificate in addition to your standard insurance card. Canada has some of the highest auto insurance minimums in the world $200,000 in all provinces except Quebec and Nova Scotia (which are $50,000 and $500,000 respectively.) Since most US states have insurance minimums under $50,000 and some states do not require insurance at all, the non-resident certificate signifies that your insurance company will cover you up to the mandatory limits while driving in Canada. Rules regarding the issuing of this certificate vary widely depending on which carrier you have. GEICO and AAA will issue a certificate valid for the entire term of your policy if you ask for it. Liberty Mutual and Progressive will only issue a certificate with advance approval for a specific date range, and some insurance companies (especially smaller local insurance companies in non-border states) will not cover you in Canada at all. If you are planning on driving into Canada, its very important to talk to your insurance company as soon as you know you'll be going.
If you are a U.S. Citizen or permanent resident and travel to Canada frequently, you may consider applying for a NEXUS card. NEXUS allows pre-approved, low risk travelers to use expedited inspection lanes both into Canada and the United States at many land crossings with minimal questioning. You can also utilize kiosks to make your customs declaration and clear the border at major international airports if you opt for an iris scan. The application fee is $50 and requires being legally admissible to both nations, thorough background investigation, fingerprinting and an interview with both U.S. Customs and Border Protection and Canada Border Services Agency.
If you intend to enter Canada using a U.S. car, take note that after crossing the border going north, the road signs change into metric units (i.e. distances are in kilometres and speed limits posted are in kilometres per hour). The usual speed limit on U.S. freeways is between 50-70 miles/hour, but you will need to read your speedometer in kilometres for the speed limit (in km/hour) once past the border, ie. 100 km/h = 62.5 mp/h. One mile is equivalent to 1.6 km so divide what you see on the road signs by 1.6 to get its equivalent in miles ie. 40km = 25 miles. If you plan on renting a car from the U.S., be sure to rent one with a speedometer that has both metric and U.S. units (a standard feature on modern U.S. cars); in this case, U.S. units are on top or outward while metric units are below or inward.
When driving within Montreal, Vancouver or Toronto keep in mind that these cities are densely populated and parking can be difficult to find and/or expensive. All three cities provide extensive public transit, so it is easy to park in a central location, or at your hotel or lodging, and still travel in the metropolitan area. You can usually obtain maps of the public transit systems at airports, subway kiosks, and train stations.
