How do I file my taxes if I worked in two different provinces in 2007?

I worked at a couple different places in Ontario between January, and September 2007, and worked at one place in Manitoba between October and December 2007.
I was residing in Manitoba on December 31, 2007, but have no documents that say so(I haven't switched over my health card or anything yet).
Also, I worked for the same company in Ontario, and in Manitoba (Loblaws.. ON- Wholesale, and MB- Superstore. I was wondering if the income from both these places will be on the same T4 since it is the same company, or seperate since they are two different places in two different provinces? What do I do if they are included on the same T4, if I must file my taxes for both different provinces? Thanks so much.

You file in your province or residence on Dec 31. You don't have to 'prove' it, it's just what you tell them. Don't lie of course, that can have massive consequences, but there is no need to document it.

That makes the question about the T-4 irrelevant, but I wonder why you don't know that, because you should have received them by Feb 29 or very soon after. You might want to contact them and make sure they have you new address.

I suspect you will get a second T4. The company is likely divisionalized with each division calculating and reporting payroll.

you file for the province of residence on Dec. 31. If you were working in Manitoba but had a spouse, children or maintained a residence in Ontario then you would still be considered a resident of Ontario. If you are still not sure which province to file for, use the one that you have provincial heath care with.