I wouldn't pay anyone to do my taxes, and don't use software that you pay for either, personally I think it's all a rip-off. You only need an accountant if you're really stuck.
Read this:
http://www.cra-arc.gc.ca/E/pub/tg/p151/README.html
Your tax home is Canada. Form 8840 is for claiming a tax treaty exemption, obviously the US does not have a treaty with itself!
If you were resident in Canada for more than 90 days in 2007 then really your only option is to basically file your
taxes the same way you did when you lived in Canada, i.e. T1 with T4, T5 etc. as you previously did. The difference is that you must file a 1040NR and an 8840 in the US with basically all the same paperwork attached that you do in Canada. The only other difference is obviously you will have a W-2 and maybe a 1099 that you also have to attach. I'm not sure what the exchange rate they use is at the moment, there is something about it in the instructions for the T1.
Yeah, you can use a 1040NR-EZ if it's simple (that form didn't exist when I lived in the US). The whole thing is a total farce imo, I always used to laugh when I filled it in. It only really matters if you have multiple sources of income and a really complex situation in the US and you have none W-2 income sources to list on the return. If you've just got a W-2 and a 1099 from the bank all you're doing with the form is telling them to send the money to the CRA.
If you have a SSN, you use that instead of an ITIN. ITINs are for people who can't get an SSN.
Bear in mind you do also have the option of moving your tax home to the US. I.e. you file on T1 that you permanently left Canada on x date and then you file a 1040 in the US covering the days you lived there. But if you do that you mustn't have any residential ties in Canada, and you can become subject to the exit tax.
The upside is that it can be less paperwork to do that (and you pay less tax usually in the US) - the downside is that if you have no residential ties to Canada, it can make renewing TN-1 status tricky so it's not a wise move unless you plan on staying a long time.
If you stay for more than five years the IRS will deem the US as your tax home anyway and that's when it gets really messy, because you have to sever all ties to avoid dual taxation.
And that's when I left!
Steve.