FMCSA and the U.S. DOT have no influence over what happens in Canada, but Canada has plenty of its own regulatory agencies and ministries whose rules will affect American carriers' privileges and ability to operate there.
With a few notable exceptions, Canadian trucking rules are nearly identical to U.S. Here are a few of the common questions about Canadian rules.
Most U.S. trailer configurations are allowed in Canada, but the 10-ft, 1-in. axle spread is frowned upon in western Canada. The overall length limit is 23 m or 75.5 feet. Some jurisdictions require permits for long wheelbase tractors pulling 53-ft trailers.
Gross and axle weight limits are more liberal in Canada, so any load that complies with U.S. interstate rules will be legal in Canada.
Canadian hours-of-service rules are more liberal than American rules. Canada permits 13 hours of driving within a 14-hour workday, and requires 10 hours off duty. Canada allows a reset, but it must be 36 hours, rather than 34. Generally speaking if you comply with U.S. HOS rules, you're compliant in Canada. And that goes for most Canadian rules, including cargo securement and the medical requirements, but there are always exceptions. Call ahead if you are unsure.
Canada does not have a federal regulatory agency like the Federal Motor Carrier Safety Administration. It has a federal department called Transport Canada, but it has little actual regulatory control. In Canada, the rules are made and enforced by individual provinces and territories. There is however The National Safety Code, which is a set of national standards supported by provincial regulations. The NSC standards establish minimum safety standards for commercial drivers and commercial vehicles licensed with a gross vehicle weight of more than 5,000 kg (12,000 lb).
American drivers and other foreign nationals working for U.S.-based carriers are allowed into Canada provided they have documentation and do not have a criminal record. It's important to note that a drunk driving conviction, including conviction under open container laws, will disqualify a driver from entering Canada as that country treats DWI as a criminal offense.
Firearms are highly regulated in Canada and must be declared when entering the country. Failure to do so could result in forfeiture and criminal penalties. Handguns are not permitted, including guns properly registered in the U.S. Different provinces have different rules relating to firearms, so call ahead if you're packing and planning to enter Canada.
Finally, since you'll be returning home some point, be mindful that U.S. Border Protection Services and Homeland Security have identity requirements for all persons entering the U.S.