Buying a MacBook from a different country, will I run into any problems?

You won't be able to add an AppleCare+ plan to a MacBook which was purchased 6 months ago. The window of opportunity to add a plan is 60 days from original date of purchase.

As long as the keyboard is appropriate (they can vary from different countries with different languages), there would no issue using the device in Canada. Warranty is international on MacBook Pro, so getting warranty coverage for the remainder of one year warranty wouldn't be an issue, unless the device would have to be replaced an exact model isn't available in Canada. Apple replaces devices with exact models purchased.

Also, you would want to make ABSOLUTELY certain your friend did ALL of the following before you buy the device --> What to do before you sell, give away or trade in your Mac – Apple Support (UK)

@babowa is correct that getting a repair may be problematic especially if the Top Case Assembly needs to be replaced as it includes the keyboard which may be unique to certain regions. It may not be possible for Apple or an AASP to acquire this part in other regions. Apple only replaces parts with the exact same part which in this case would be one including the exact same keyboard. Keep in mind the Top Case Assembly includes a lot of other components such Keyboard, Trackpad, Battery, and sometimes Touchbar and Speakers. I don't think you would have a problem getting international service for any other component. Read the AppleCare agreement carefully since Apple does mention that some repairs may not be available for a Mac purchased in other regions.

It would be safest to purchase a laptop from the region you live in (or will be working in the most) if you want to have a timely repair.

You cannot buy Applecare for a used device and, even if you could, Apple may restrict service to the country it was originally purchased in. The one year warranty is worldwide, but you may or may not encounter problems getting service in other countries due to parts shortages, etc.