Canada will not extradite unless the offence stated is an 'indictable offence', had the crime been committed in Canada. Harrassment is likely a misdemeanor in the United States, but not so in Canada apparently, so Canada will say, "Hey, this American here has a warrant out on him in the US for a harrassment charge which is a misdemeanor over there. Never mind that, because we consider it a felony here in Canada (felony in Canada is termed an indictable offence). Heck, let's deport him! We don't want him here!" Yes, that's how it works and that is what will happen sooner or later.
You'd be better off facing this charge and getting a good lawyer.
However, barring that, you'll do better moving to another state in the US rather than residing in Canada, since many US states won't extradite over misdemeanors.
You can however be detained by the police in any state for this outstanding warrant and they can contact the state where the warrant originated. Then that state with the warrant can decide to extradite or not. Sometimes they will extradite, but I doubt they would. Then the host state may not allow them to take you back unless the requesting state pays for all of it.
Everytime you get pulled over by the police, they usually run NCIC on you and they will find it and then bother you at the least, or jail you at the worst, regardless of whether you can be extradited or not. You will keep facing the prospect of being detained or at least harrassed by law enforcement until you settle this.
Harrassment sounds like a small charge. Just get it taken care of. I mean, how bad is it? Usually first offenders get probation and a fine.
The maximum for most misdemeanors is 1 year in the county jail. Some have up to 2 years for aggravated or "high" misdemeanors.
I doubt you would see more than a few weeks in jail.
