If you are not a US person (resident alien or Citizen) you should not complete the W9. You would complete a W8.
If you are in the US performing this work the IRS requires that you file a US return and you will need an ITIN to file or open a bank account.
You can apply for an ITIN by filing form W7.
If you want to open a bank account in the US they generally require a Tax Number (ITIN)
By completing the W8 you are saying that you are not doing this work in the US so no US tax is on you for this work performed in Canada.