US Residents will need a passport to travel to Montreal. You should plan to have your passport in hand no later than 3 months prior to the conference. Information about obtaining and renewing passports is below.
Applying for a Passport (opens in new tab): https://travel.state.gov/
Renewing a Passport (opens in new tab): https://travel.state.gov/
Canadian Work Visa Information (opens in new tab): http://www.cic.gc.ca/english/visit/business.asp