It depends on if you plan to return to NH after working in Canada, whether you own a home in NH, whether NH is where you vote and have a driver's license. It is a domicile state. See below for a link regarding NH and domicile.
Residency Status for New Hampshire.
Residents. Residency is based on domicile in New Hampshire. Factors considered in determining whether the taxpayer is a resident of New Hampshire includes:
•Maintaining a home or living quarters in New Hampshire.
•Spending a greater percentage of time in New Hampshire than any other state.
•Having family living with them in New Hampshire.
•Advising a governmental agency that the taxpayer considers New Hampshire his resident state.
•Having employment or business activities either in New Hampshire or in a location that is easily commuted to from New Hampshire.
•Registering to vote in New Hampshire.
Part-year residents are individuals who have either permanently established or permanently abandoned residency in New Hampshire during the year. Temporary absences do not affect residency.
Please see attached for more information on domicile for NH http://www.nhpublaw.org/nh.law.about/law/70
