Terry, you have had no response to your question so I will chip in with my poor understanding of the issue. I did Canadian taxes, personal and corporate for about 5 years and that included 3 cases of joint US and Canadian filing.
First, get some proper advice – HR Block is surprisingly good for their price and can at least get you started.
Read the following link:
http://www.americanlaw.com/ustxtmp2.htmlIf at all possible avoid getting dragged into the maw of cross border taxation. Here is a situation where having a corporation perform the photo work is far easier than a simple person.
All the galleries I have worked with have done their best to avoid paying you anything and will use any excuse. I hope you are not in this situation because you have bigger problems to deal with.
We don’t know the length of the gig so I am guessing here, but based upon the “americanlaw” link above you are likely to be a “non-resident alien” as far as the US is concerned and are therefore NOT taxable in the USA.
This comment is based on the “Substantial Presence Test” since I doubt that you spent more than 31 days on this gig in the US. If the job is just selling them prints rather than being in the US working for the gallery then you are not taxable in the US anyway (except perhaps for sales tax). Do all you can to avoid W7s and ID numbers, you do not need them.
If my guess is correct, then your issue is then getting the gallery to accept a statement that you are a “non-resident alien”. HR Block should be able to help you with a proper declaration.
Note that even if you avoid US taxes, you are supposed to file your Canadian taxes on your World-wide income, so you should be reporting your US earnings on your T1 or T2.
Good Luck.