Well, becoming a sub-contractor means you have to set up your own business in Canada!
It sounds as though your US business is quite small but on the other hand you have control of it.
There are two ways of doing it, either the US business registers itself with the CRA and gets a business number so it can do payroll and GST, or alternatively you either register as self-employed or set up a CCPC and invoice the US company. Then you do the payroll and GST yourself. But either way because you own the US business it sounds as though you're going to be doing it yourself.
It really depends on the nature of the business in the US, if it has lots of employees and you're just a one-off, probably better to just go the self-employed route in Canada. If you're doing all the tax paperwork for the US company you might as well just get it a business number and do it that way, although this can get complicated because expenses to the company have to be charged against the income from each country.
How to do your personal
taxes is a bit of a tricky one, a spouse is a residential tie for tax purposes. Also married couples can only have one principal residence, which means the other one becomes subject to capital gains tax.
Given that you're both US citizens, you have to file 1040 jointly if you're married (regardless of where you live), although I think it is possible for one of you to be non-resident and file a 2555 so you don't get taxed twice, you'd have to check with the IRS on that one.
So in essence if only you move to Canada, you would register as self-employed and file a T1 as a single self-employed person, and you would file jointly on 1040 in the US, you would file a 2555 to exclude your Canadian-source income from US
taxes. You would invoice the US company and they would pay you. GST is zero-rated for whatever you bill the US company but you still need a GST number.
There's no need for all the other forms people usually need like 1040NR, 8233 and so on because you're a US citizen and have to file 1040 every year anyway.
That's one way of doing it anyway, I can think of about half a dozen other ways, but if you're a two-person company that's probably the easiest.
Steve.