You need more information here. 
1. Are they both US citizens? 
2. Did they both have income? Who/how much/where

one is a u.s resident who lives in GA and has income in GA.The other one is not, lives in Canada and has income in canada.  They want to file married filing separately.  What forms should i use to file federal and state?

Assuming you mean the state and not the country of Georgia, does the US resident have any dependent children?  Is the Canada resident in Quebec, which from what I can figure out recognizes community property, although I'm not sure how that affects taxes?  Does the Canadian resident have a US green card (resident visa, even if not a resident)?

Here is a link that will help you decide: https://www.irs.gov/individuals/international-taxpayers/nonresident-spouse