I traveled to the USA for about a month before I came to Canada on a working holiday visa. I didn't leave North America. Am I still able to go back to the USA? I have been told that I can't, that I would need to leave the continent.
I'm going to assume you entered the US under Visa Waiver Program, since this is a fairly common question in those circumstances. If you entered the US on a visa, then you are allowed to enter the US again no matter how long you were in Canada, provided your visa has not expired and it permits multiple entry.
A VWP allows you to remain in the US for 90 days, and there is a well known rule that exiting to Canada does not reset that clock. However the purpose is to prevent someone having multiple back-to-back 90 day visits by making a 'visa run' to Canada. There can be exceptions if that is clearly not what you are doing.
If it is less than 90 days since you entered the US, and you can show that you intend to leave the US before 90 days from the day you first entered, you can re-enter the US on the same visa waiver. This will not be a problem.
If it is more than 90 days since you first entered the US, or you intend to stay beyond 90 days since you first entered, you will need to get the border officer to issue a new visa waiver for you. Officers can do this on a discretionary basis. Whether they do or not is going to depend on how long you were in Canada, and how long you were in the US before that. If you were in Canada for several months this should not be a problem (you may need to provide evidence of this fact, particularly that you left the US when you say you did). Evidence that you intend to leave the US after a short time will also help your case.
The bottom line is that if you don't look like you are trying to game the system and extend your stay in the US then you will probably be let in.